This will give you the results you need for the Flex data and accounts for loss then improvement, or improvement then loss, constant improvement, or constant loss.
Formula:
=IFERROR((INDEX(tblROM[@[Wk 1 Flex]:[Wk 4 Flex]],1,COUNT(tblROM[@[Wk 1 Flex]:[Wk 4 Flex]]))-[@[Wk 1 Flex]])/[@[Wk 1 Flex]],"")
It will also mean the average in I15 doesn't have errors to contend with.
With the Ext data how do you want to reflect somebody who starts at 0 and ends at 3? Compared to somebody who starts at 0 and ends at 2?
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