Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 5 years ago.
Improve this question
Im the context of pair-programming ...how do you estimate? A 5 point story ...split in to 3 tasks...each task being swarmed by 2 members. Does it mean it mean it is finishable in half the time?
You estimate using points. The number of points achievable by a pair is called velocity. Check this: http://en.wikipedia.org/Planning_poker
I always stress story sizing over estimating. If you can minimize the variation in size between stories, then estimates become much less interesting. That is, estimation activities lose their value when the difference in size between any two stories is small, which helps fast teams recoup the cost of estimation and put it toward something productive (like building product).
With that in mind, I would suggest proactively pruning the backlog and splitting five point stories into smaller ones (still thin vertical slices) whenever possible. Until your team is experienced, I'd suggest you continue to have estimation parties, but prompt a default estimate of 1 point to each card, with a quick consensus check or discussion as to why any justify a bump to a 2 or 3. For anything that's clearly bigger than a 3, I'd suggest challenging that one of two problems is present: the baseline value of "1" is too small or the story should be split (either made more specific or tracked as an epic).
As the team establishes a decent velocity, the activity can hopefully shift its mindset from estimation to mere story vetting. That is, the question during planning of "how big is this story?" becomes "is this story abnormal?" The latter question takes significantly less time to answer.
Most Agile methodologies suggest that you should estimate in points. However, there are many successful teams out there - including several advanced and highly productive Kanban teams - who estimate in hours. Points come with their own games, perverse incentives and problems. YMMV. Anyway...
I've heard figures of 25% more dev-hours for a pair completing a task. So, the task would be finished in 62.5% of the time, using two developers instead of one. However, the quality of and knowledge-sharing often increases too. Since bugs = rework and rework takes longer than doing it the right way the first time, pair-programming usually pays for itself. This differs for different tasks and levels of skill, eg: simple bug fixes, novice programmers, etc.
In my experience 2/3 of the time is a pretty good ballpark figure. It's longer than 1/2 but less than it would be with just 1 person.
Sallyann Freudenberg is a good name to look up regarding pair programming research. You could also check out the refs on the Wikipedia page:
http://en.wikipedia.org/wiki/Pair_programming
The figure is mostly borne out by the data in this report by Alistair Cockburn and Laurie Williams: http://collaboration.csc.ncsu.edu/laurie/Papers/XPSardinia.PDF
Pair estimates how long it is going to take them. Any estimate is based on experience - the longer experience team has with the project, with technology and with working together in pairs the better the estimates will be. Any arbitrary percentages like add 25% for pairs etc. are of any use only at the very beginning - with new project and new team on new technology - where you have nothing else to base estimation on yet. As soon as experience starts building the estimates will improve.
Remember though, that they are just this - estimates, that is our best guess of the future derived with the help of experience and knowledge from our understanding of the present. It's like weather forecast - the more data we have, the more experience forecasters have the better it is, but it is just a prediction, not reality.
Which is why points are so great, because they help you estimate one parameter you can - how "big" the tasks at hand are.
1) A simple, concrete way to think about estimating units is the number of check-ins it would take to complete the story.
If you're doing TDD, continuous integration and refactoring you'll be working in small, chunks of work, keeping the build green and checking in regularly so under those conditions single check-ins can be a meaningful unit of estimation.
2) Alternatively, think about blocks of uninterrupted pairing time in a day e.g. after stand-up to coffee break, after coffee break to lunch, after lunch to mid-afternoon break, mid-afternoon to going home time - say 4 periods a day.... so say 4 units is a single day. That gives you a bound on what you could expect to do in an interation...
Personally I go for the number of check-ins, because I can sketch out roughly the tasks involved and get an idea of check-in numbers.
The great thing about number of check-ins is that it doesn't matter if you're pairing or not - you're just tracking what you can get done.
Related
Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
This question does not appear to be about programming within the scope defined in the help center.
Closed 5 years ago.
Improve this question
I understand that on the first part of your sprint planning, you would size the stories for example using story points and poker cards and then you estimate how many stories you can tackle on the next sprint. So let´s say you agree on working on 3 stories with a total combined of 18 story points.
Then you go ahead with the second part of the sprint planning and you start breaking those stories down into tasks. These tasks are now estimated using actual hours.
I have two questions:
1) How do you estimate the tasks in hours? do you use again poker estimating but with number of hours this time? how does the team agree on the number of hours for each task.
2) Once you estimate all tasks for the 3 stories you agreed for the sprint, you find out that the number of total hours combined for all tasks of all 3 stories is 90 hours for example. If your actual team capacity in hours is 75, how do you adjust your initial commitment of delivering 3 stories now that you realize that you don´t actually have the time to do it? Do you go back to your Product Owner (if he´s not there anymore) and tell them that you will be delivering 2 stories instead or how do you go about this?
Thanks a lot in advance for your help!
The tasks are not really estimated in hours but ideal hours. It's really hard to predict how many ideal hours will be available in a week, and it's generally not a good idea at all to infer the capacity on a sprint based on hour estimates. See for example this Scrum Alliance blog article
Story points and task hour comparison can be thought of as the comparison of the weight and height of an elephant. In general, a taller elephant may be heavier than a shorter one, but this is not always the case. There is no biological proof of a weight-versus-height formula, despite the common perception that more height means more weight. The same explanation applies to story points versus task hours: In general, a more complex user story (higher points) should take more hours to complete, but there are always exceptions.
Normally, tasks are tackled by a single team member (or a pair), and thus they are estimated by them, and not by the whole team.
Furthermore, tasks are re-estimated daily: the number we look for is the number of ideal hours left to complete the task and not the total amount. So, it is a number that can go up or down, or remain constant.
Also, tasks can be added or removed during the sprint. It's actually pretty common to discover that initial plans change. It doesn't matter, as long as the total number of hours planned represents the best current estimate of what's left to do -- it's needed for burndown charts.
In conclusion, don't mind the hours. Use them to monitor progress during the sprint but not to determine capacity. This is what points are for and the two parameters are not interchangeable as it would seem.
In my experience, breaking into and estimating tasks is very useful and often underated. The idea is that the team become more and more accurate as time goes on through their sprints and they inspect and adapt. I have observed teams getting to the point where they end up completing everything in the sprint except for unforseen blockers (eg. Server down time). The idea is that the team calculate their capacity in (hours) and then calculate the amount of tasks they need to complete ( in hours). They can use this as a guide to make a commitment. There is a more detailed explanation here: http://www.pashunconsulting.co.uk/team_commitment_blog.html
You can also use story points to make a commitment but the general principle is that Story points are better for long term estimation (ie. for estimating when the project will deliver). Agile Estimating and Planning is a good book for this kind of stuff, as is the Scrum Mega Pack.
I guess an issue come from the assumption that you are able to deliver 18 points within a sprint. What looks not right when you do an estimation in hours later. So, commit to fewer number of story points initially and after several sprints you would be able to know your actual velocity in story points per sprint.
While breaking stories into tasks is helpful, it is not very useful to estimate those tasks.
The reason is that you will spend a lot of time doing these micro estimates and they will generally be inaccurate.
Besides, adding concrete hourly estimates forces work to fit in those estimates.
If you underestimated you might procrastinate, if you overestimated you might skip on reviews, unit tests or other quality practices just to fit the timeline.
So in general I like to stay with one estimate level -> the one that gives the velocity.
Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 5 years ago.
Improve this question
I am used to thinking about time estimates in the way suggested by Joel Spolsky - that if a scheduled item takes more than 16 hours, it should be divided into smaller tasks. Now, I am implementing Scrum in my team together with Story Points based estimations. It seems to me that a good unit for a Story Point would be ideal man-hour, not man-day. If I used days, most of my issues would have estimates 1/2 or 1.
Do you have any idea, why the use of ideal man-days is mentioned most often in the Scrum literature?
It seems to me that a good unit for a Story Point would be ideal man-hour, not man-day.
This phrase sounds really, really strange, and not true. Where did you read that there is a correlation between Story Points and ideal man-day? Ideal man-days were maybe used in the early days of Scrum but, to me, Story Points (SPs) are a different thing...
Story Points are a way to to quantify the relative effort associated with a particular Product Backlog Item (PBI) which is composed of multiple tasks. Some teams use numeric sizing (i.e. a scale of 1 to 10) to estimate the "size" of a PBI, others use t-shirt sizes (XS, S, M, L, XL, XXL, XXXL), some use the Fibonacci sequence (1, 2, 3, 5, 8, 13, 21, 34, etc). And by the way, did you notice that SP are unit-less?
If I used days, most of my issues would have estimates 1/2 or 1.
So what? That would just mean that you have small PBIs, which is not a bad thing (at least not for the most important one). But don't forget that there are theoretically two level of estimation in Scrum: the Product Backlog level, in points, and the Sprint Backlog level, in hours. As I mentioned in the previous paragraph, PBI are composed of tasks and they should be split into tasks during the second part of the Sprint Planning Meeting. And tasks are then estimated in hours and the 16h rule applies here: a task should not exceed 16h. If it does, it is too big and should be split into smaller tasks (because we are too bad at estimating big things).
Do you have any idea, why the use of ideal man-days is mentioned most often in the Scrum literature?
This is outdated anyway. Things might change in the future but the current consensus is to estimate in unit-less points. Points are entirely decorrelated from any time unit and this is intentional to avoid any mapping with real world unit, work capacity should be measured with the velocity (the amount of points a team can achieve in one iteration).
Estimating at the hour level is too fine-grained. It also will tend to drive to over micro-management, which is somewhat antithetical to agile principles.
If I have four tasks, each estimated at a half day, I can be relatively confident that in two days I'll have a good handle on them.
But 16 1-hour tasks? I have much less confidence in those being done in the same period of time, as any one of the tasks is subject to way too much variability.
The purpose of story points and the estimating game in general is to effectively judge velocity over several sprints.
So it doesn't actually matter what units are used to estimate, so long as everyone on the team estimates in the same way, and the same units are used at each estimation session.
It's also very important to make sure that different teams don't try to correlate their story points. What I think of as a story point won't necessarily be what yours is.
So - I can't provide an answer other than "go with what seems appropriate".
Googling for "scrum ideal man hour" gives 6500 results while "scrum ideal man day" gives 10000 results. Not that big a difference. I haven't noticed a bias towards either in the literature.
Nothing really valuable rarely gets done in less than half a day (min. task duration) or even a week (min. sprint duration).
Estimating in hours can give a false sense of accuracy. Even though 5 ideal man hours is precise, it's probably not any more accurate than 0.5 ideal man days.
Ideal man units also convey the notion of mapping to real world similar units such as hours or days. The mapping is rarely straightforward. That's why many agilists prefer unitless story points as a task size measure. Team velocity metric then does the mapping from abstract size estimates to real world time.
If you're following proper Agile practices, with full unit test coverage and the red-green-refactor cycle, there are a vanishingly small number of meaningful tasks which will take less than half a day. Also, using days counteracts the developers' tendency to underestimate the time required for a task. And of course, it's better to over-estimate times and over-deliver than to under-estimate and under-deliver.
I don't know but I'm prepared to speculate that this is because the "standard" scrum length is 30 days. If you're planning to do work in blocks of 30 days then you're going to need coarser units of measurement than if you had a sprint length of 1 or 2 weeks.
Most of the scrum implementations I've seen have spring lengths of 1 or 2 weeks - so counting "ideal hours" is more useful because the relative task sizes are smaller.
As far as a relative measure of effort is concerned and assuming you're using scrum to develop software I'd count the number of separate source code commits you could make if you developed each task cleanly and use that as a measure.
Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
This question does not appear to be about programming within the scope defined in the help center.
Closed 5 years ago.
Improve this question
I've been learning Scrum and trying a tool called Acunote for use with it. My question is about two fields I have there, for each task. They're "estimate" and "remaining". What unit should I use for those? Do I use Story Points? What about the remaining? For example I have a task that will take 10 units, let's say. I fill the remaining at the end of day with how many "units" I believe it will take me to complete?
Thanks!
I have a few suggestions for you:
If you are new to scrum; use a whiteboard and don't get bogged down in a particular tool's semantics; it will hamper your learning and adoption.
Break your stories small enough so that you don't have to create and estimate Tasks.
Don't do anything with hours, it is a waste of time to estimate at that level.
Burn down story points.
It is all too easy and common for teams to "think" they are on track because Tasks are being completed and burned down. Then they get to the end of the sprint and find that 5 stories are all 90% done and nothing is completed. If you burn down stories you are actually tracking deliverable business value and not just an arbitrary amount of developer-junk.
As always, my first advice would be to not use a tool when adopting/learning Scrum (I start to be tired to repeat the same thing over and over :). Instead, start with the simplest thing that could possibly work (a spreadsheet for the Product Backlog, a white-board and post-it notes for the Sprint Backlog). The rationale behind this is that you want to learn and master Scrum, not a tool. So don't let a tool tell you how to do Scrum and drive the process.
Then, regarding the question, there are 2 schools of thought: 1. what Scrum says in theory, 2. what some people do in practice.
In theory, Scrum has two levels of estimation: one for work (Tasks) to be completed within the current Sprint and one for more distant Product Backlog Items (PBIs). At the Product Backlog level, items (the "what" is being built) should be estimated in Story/T-Shirt/Unit-less points which have a low degree of precision. This approach avoids "analysis paralysis" pitfalls and accurately reflects the general uncertainty surrounding the work in question. At the Sprint Backlog level, items are beaked down into tasks (the "how" a PBI will be achieved) that are estimated in hours. A separate estimation scheme is appropriate because Tasks describe granular work (usually on the order of a few hours, never more than 16h). In fact, Scrum recommends using "ideal engineering hours" for Task-level estimates.
In practice, some people don't estimate in hours because burning down hours doesn't show "real" progress, which isn't false, and they prefer to burn down Story Points (which really means an item is done or not, it's more binary).
While I understand the "spirit" of the later approach, I don't apply it and stick with the theory. Actually, for the reasons previously mentioned, estimating in hours does make sense to me and I actually find that it gives better "control" of the Scrum empirical process during a Sprint (at the end of each day, you should update the estimated remaining work regardless of the actual time spent and this is easier with hours).
Moreover, I don't like the drawback of having only small stories (which can be seen as waste too) but like when a team identifies clearly what has to be done within a Sprint (this is good for transparency and helps the Product Owner to understand the real amount of work too, especially "quality oriented" tasks).
Finally, I think that you can avoid the pitfalls mentioned by DancesWithBamboo with hours too. Just stay vigilant and:
Always focus on the most important PBIs (and related tasks) first.
Pay a special attention to non-finished tasks, they should keep moving on the white board (if you are using columns to represent steps like for example "todo", "in progress", "to be verified", "done"); a non moving task is a smell.
Don't start a new item before the previous is done.
So, in my opinion, it is possible to use hours and to avoid the "nothing done" at the end of the Sprint syndrome. Just use your brain (Scrum and/or any tool won't replace it, luckily for us).
Having that said, and if you don't throw your tool away, the questions to answer are: what do you want to show on the burndown (points or hours depending on if you breakdown the work into tasks or not, I gave you my point of view) and what field does Acunote use to draw the burndown (i.e. where should I update the estimation of the remaining work). If you choose points and don't use tasks, it wouldn't make sense to update remaining work unless it's totally done IMO (a PBI is done, or not).
IMHO you shouldn't use remaining for the SCRUM points, because the points should be really subjective and you probably can't say how far you have gone.
I would recommend that you break the task into smaller ones (these ones would be the steps you need to implement the features) and then estimate them into hours. This way you can easily track the progress of the feature
Use hours for both the initial estimate and the remaining time. Tasks are usually estimated in hours.
You can use Scrum point - or any other unit - to estimate the backlog items.
I would not bother with remaining. A story or a task is boolean (either done or not done).
In our team we started to accept only tasks that are expected to have less than a day. That way no team member should be working on the same task on two consecutive daily scrums. The third day for sure rings alarm bells!
Also breaking up in task is easy and fast, because it doesn't take much estimating. Is it less than a day: OK, otherwise break it down.
Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
This question does not appear to be about programming within the scope defined in the help center.
Closed 5 years ago.
Improve this question
with agile estimating, is it true some say to choose intervals like 1/2 to 1.5 days only?
It tends to be a good rule of thumb (agile or not) that your tasks should be broken down into at most 1 - 2 day increments.
The idea is that if you have larger chunks than that then you haven't broken the task down enough and you will more likely miss the estimate and miss it by larger amounts of time than had you broke it down. Often when you break it down you discover your initial estimate was off and since you have broken the task down into more concrete tasks your estimate is now more accurate, more trackable and meaningful.
For tasks that are coming up on your to do list soon you should pay attention to this but for long range planning where you haven't necessarily thought out the feature in detail I think larger estimates / tasks not broken out for the feature is OK.
Here's a link to Joel Spolsky talking about this. Take a look at item #5 about half way down the page.
http://www.joelonsoftware.com/articles/fog0000000245.html
In my experience, any estimate that's longer than 2 days is probably hiding serious work that should be broken down further. Such estimates have a very high probability of going over. Try to break everything down into smaller chunks so that no individual chunk costs more than 1-2 days.
There are advantages to keeping the estimates short. It forces you to break up large tasks into small, discrete tasks that can be measured and discussed quickly, which helps promote the entire Agile development process.
That being said, I almost never keep a "rule" as a hard and fast rule with things like this. I'd say this is a good guideline, however.
My team consists of junior programmers (university students) and we've found that it's generally easier if we break all the large tasks down into a bunch of smaller ones. It involves more forward-thinking but in the end we are more productive and can it's easier to evaluate our progress. It also brings a sense of achievement when you have something completed at the end of the day.
I would agree with that guideline. Anytime I have ever taken on a 5 day task, it has degenerated to a three week nightmare. Large estimates indicate you didn't learn enough about the problem up front to know what is involved, because if you had, you could have found ways to break it up better.
I don't agree. If a team's iterations are two week long, the 10 days mean that 1 day would be spent for iteration close (show & tell), iteration planning and tasking or planning poker.
When playing planning poker, a team either geometric or Fibonacci progressions for estimates. For example, cards would contain values such as 1, 2, 4, 8, 16 or 1, 2, 3, 5, 8, 13. Each number reflects the number of days of development for a pair of programmers.
For each card, once discussion has occurred, each member simultaneously plays the card that reflects their estimate. If the majority of the team converges on the same estimate, the estimate is accepted. If there is much variation in the estimates, further discussion occurs (members explain the reason for their estimates) and another round of voting takes place. This occurs until consensus is reached.
If a number greater than 8 is picked, then the card is deemed to be too big and the card is refactored into at least 2 smaller cards. The reason being is that such a large estimate indicates the card is too big to be completed in a single iteration and any estimate is very likely to be inaccurate.
Using such a method brings commitment from the team members to delivery all they have committed to and for a new team the estimate become so accurate that carry over of cards soon become a low risk.
A very good post about agile estimation and planning you can find on the blog of agile42: Just enough, just in time
A lot of good answers here, so I'll play devil's advocate and approach it from a different side.
There's a possible problem with breaking down things into very small estimates (# of hours) when doing things such as release planning. David Anderson discusses it in his (excellent) book Agile Management for Software Engineering.
Basically, the idea is that with a task that is very small, a developer will pad his estimate by a fair bit (say, turning a half hour into an hour, or doubling it) because of a certain amount of ego that would be bruised if the developer failed to complete such a small task in the estimated time. These local buffers add up quite a bit and result in a global buffer that's far bigger than it needs to be.
This is less of a problem if you stick with .5 days as a min - it's basically assumed that there's some buffer in there, so you won't need to pad it any more.
I feel there is a bit of mix of information and overlapping in this thread... allow me to make my point :-)
1) The Fibonacci sequence, that is very much use through the Planning Poker technique from Mike Cohn, is about estimating "Complexity" of User Stories, which are - as Cam said - normally written on cards, and entail more than one task, at least all of those which will be needed to make a Story shippable (Ken Schwaber, Alistar Cockburn, Mike Cohn...)
2) The tasks that are included to complete a Story, are normally estimated in Ideal Hours or Pomodori (Francesco Cirillo, "The Pomodoro technique"). If you estimate in Ideal Hours normally the rule of thumb is to keep them between 1/2 day (3 ideal hours) and 2 days (12 ideal hours) of work. The reason for this is that doing so the team will have more qualitative status information by having at least every two days a team member reporting a Task as done, which is much more "valuable" than a 60% done. If you use Pomodori they are implicitly "timeboxed" to 25 min. each
The reason to keep tasks small comes basically from the "Empirical Process Control Theory" for which through transparency and regular inspection & adaption, you can better check the progress of your work, by quantifying it. The goal of having smaller tasks is to be able to clearly describe and envision in details what will be actually done, without adding too much of "guessing" given to the natural uncertainty deriving from having to predict "the future". Moreover defining an outcome and a shorter timebox allow people to keep the focus with enough "sense of urgency" to make it a challenging and motivating experience.
I would also catch up the point of the "motivation" and "ego" - from Chris - by adding that a good way to have people committed and motivated is to define the expected outcome of a task, so to be able to measure the results upon completion, and celebrate the success. This idea is encapsulated in the Pomodoro Technique, but can be achieved also using ideal hours for estimation. Another interesting part of the Pomodoro Technique is that "breaks" are considered "First Class Citizens" and planned regularly, which is very important especially in creative and brain intensive activities :-)
What do you think?
Best
ANdreaT
Closed. This question is off-topic. It is not currently accepting answers.
Want to improve this question? Update the question so it's on-topic for Stack Overflow.
Closed 10 years ago.
Improve this question
Having used "days" as the unit for estimation of tasks in Scrum I find it hard to change to using Story Points. I believe story points should be used as they are more comparable to each other - being less dependent on the qualifications of whoever addresses the task etc. However, it isn't easy to make a team start using Story Points when they're used to estimating in days.
So, how to make a team change to Story Points? What should motivate the team members to do so, and how should we apply the switch?
When I switched to points, I decided to it only if I could meet the two following points; 1) find and argument that justify the switch and that will convince the team 2) Find an easy method to use it.
Convincing
It took me a lot of reading on the subject but a finally found the argument that convinced me and my team: It’s nearly impossible to find two programmers that will agree on the time a task will take but the same two programmers will almost always agree on which task is the biggest when shown two different tasks.
This is the only skill you need to ‘estimate’ your backlog. Here I use the word ‘estimate’ but at this early stage it’s more like ordering the backlog from tough to easy.
Putting Points in the Backlog
This step is done with the participation of the entire scrum team.
Start dropping the stories one by one in a new spreadsheet while keeping the following order: the biggest story at the top and the smallest at the bottom. Do that until all the stories are in the list.
Now it’s time to put points on those stories. Personally I use the Poker Planning Scale (1/2,1,2,3,5,8,13,20,40,100) so this is what I will use for this example. At the bottom of that list you’ll probably have micro tasks (things that takes 4 hours or less to do). Give to every micro tasks the value of 1/2. Then continue up the list by giving the value 1 (next in the scale) to the stories until it is clear that a story is much bigger (2 instead of 1, so twice bigger). Now using the value '2', continue up the list until you find a story that should clearly have a 3 instead of a 2. Continue this process all the way to the top of the list.
NOTE: Try to keep the vast majority of the points between 1 and 13. The first time you might have a bunch of big stories (20, 40 and 100) and you’ll have to brake them down into chunks smaller or equal to 13.
That is it for the points and the original backlog. If you ever have a new story, compare it to that list to see where it fits (bigger/smaller process) and give it the value of its neighbors.
Velocity & Estimation
To estimate how long it will take you to go through that backlog, do the first sprint planning. Make the total of the points attached to the stories the teams picked and VOILA!, that’s your first velocity measure. You can then divide the total of points in the backlog by that velocity, to know how many sprints will be needed.
That velocity will change and settle in the first 2-3 sprints so it's always good to keep an eye on that value
If you want to change to using story points instead of duration, you just got to start estimating in story points. (I'm assuming here you have the authority to make that decision for your team.)
Pick a scale, could be small, medium, large could be fibonacci sequence, could be 1 to 5, whatever pick one and use it for several sprints this will give you your velocity. If you start changing the scale from one to the other then velocity between scales is not going to be comparable (ie dont do it). These estimates should involve all your Scrum team.
Having said that you still need an idea of how much this is going to cost you. There arent many accountants who will accept the answer "I'll tell you how much this is going to cost in 6 months". So you still need to estimate the project in duration as well, this will give you the cost. This estimate is probably going to be done by a senior person on the team
Then every month your velocity will tell you and the accountants how accurate that first cost estimate was and you can adapt accordingly.
Start by making one day equal one point (or some strict ratio). It is a good way to get started. After a couple of sprints you can start encouraging them to use more relative points (ie. how big is this compared to that thing).
The problem is that story points define effort.
Days are duration.
The two have an almost random relationship. duration = f ( effort ). That function is based on the skill of the person actually doing the work.
A person knows how long they will take to do the work. That's duration. In days.
They don't know this abstract 'effort' thing. They don't know how long a hypothetical person of average skills will require to do it.
The best you can do is both -- story points (effort) and days (duration).
You can't replace one with the other. If you try to use only effort, then you'll eventually need to get to days for planning purposes. You'll have to apply a person to the story points and compute a duration from the effort.