SUM and OFFSET Summary tables

[drluke]

	SUMMARY
	A	B	C	D	E	F	G
1	8-YTD	January-August 2018
2	Number	Name	Bal b/f	Sales	Returns	Adj	Total
3	101	Coventry
4	102	Liverpool
5	103	Cardiff
	In a second sheet - DATA2018 - I have 3 tables with data for Jan - Dec for each of Sales, Returns & Adj. I also have a table for opening balances.
	A1 is a dropdown from a list. For every month there are 2 selections available in the list: (a) data for the period only; (b) data for the YTD
	I want to summarise data in my data tables based on the selection made from the dropdown in A1.
	Bal b/f if A1=1: simple lookup to the op balance table
	Bal b/f if A1=anything else: opening balance + sum of Sales, Returns & Adj for all prev months for all numbers in A3 down
	I won't ever have to calculate opening balances for Sales returns or Adj
	For the other 3 types of transactions if eg A1=6, then just show the totals for June from the data sheet, but if A1=6-YTD then I need to show the total of Jan-Jun for each
	In my data sheet the data is arranged in tables like this:
	A	B	C
1	Number	Name	Bal b/f
2	101	Coventry
3	102	Liverpool
4	103	Cardiff
	SALES
	A	B	C	D	E	F	G
105	Number	Name	Jan-18	Feb-18	Mar-18	Apr-18	May-18	etc
106	101	Coventry
107	102	Liverpool
108	103	Cardiff
	Returns start at A205 and Adj at A305
	I thought that I could use INDEX-MATCH to find the numbers in A2 etc of my summary sheet, and use SUM+OFFSET to fill out the data, but really not sure what the best way is to do this summary.

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