Formula logic for extracting specific cell data - excel

Question

For extracting First £ figure and not the second one from sample data
(24M UNLTD+INS 30GB £347+£30 S6)
Following array formula has been used in Stackoverflow questions.
{=MID(A1,FIND("£",A1),MIN(IF(ISERROR(MID(MID(A1,FIND("£",A1)+1,999),ROW($1:$999),1)+0),ROW($1:$999),999)))}
I attempted an analysis of the formula as represented in the image below. I am not able to grasp the logic of part
MIN(IF(ISERROR(MID(MID(A1,FIND("£",A1)+1,999),ROW($1:$999),1)+0),ROW($1:$999),999))
As to how it leads to a figure of 4. Request that this part of formula be elaborated to clarify the role of various constituents of this formula.

Answer 1

Try the following as a standard (non-array) formula,
=--REPLACE(REPLACE(A2, 1, FIND("£", A2), ""), FIND("+", REPLACE(A2, 1, FIND("£", A2), "")), LEN(A2), "")
First the inside REPLACE(A2, 1, FIND("£", A2), "") erases everything up to the first £ symbol, then the same logic is applied to erase everything in that modified text from the first + to the end. The -- converts text-that-looks-like-a-number to an actual number.
The array formula you provided uses a more convoluted logic.
FIND("£", A2) + 1 finds the starting point of the first number after the first £ symbol. e.g. The first £ is the 20th character so it returns 21.
MID(A2, FIND("£",A2)+1, 999) extracts the text following that first £ symbol. The text might look like it starts with a number but it is text masquerading as a number. e.g. 347+£30 S6
In an array formula, ROW($1:$999) processes as a sequence of numbers from 1 to 999, incrementing by 1 for each cycle of calculation.
MID(MID(A1, FIND("£", A1) + 1, 999), ROW($1:$999), 1) + 0) returns an array of text values, each one 1 character long and 1 position deeper into the text than the previous one. e.g. 3, 4, 7, +, £, etc.
+0 is used to try and convert each of these pieces of text to a number. The IFERROR function returns TRUE if a piece of text cannot be converted to a true number. The first one that cannot be turned into a true number is the 4th e.g. +
The IF catches the TRUE on the fourth position and returns 4 from the second ROW($1:$999). It has returned 999 for positions 1, 2 and 3. e.g. 999, 999, 999, 4, 5, etc.
The MIN catches the smallest of these numbers returned as an array. This is where the 4 comes from. e.g. 999, 999, 999, 4, 5, 999, ...
You can see this yourself by changing all of the 999's to 9 then using the Evaluate Formula command. The reason changing to 9 is important is so that the returned arrays of number look like 1, 2, 3, 4, 5, 6, 7, 8, 9 which does not obfuscate the results quite a badly as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, ... 998, 999.
        This shows the formula evaluated several steps into the process. Note the 4 being returned to the MIN function.