Understanding the Autosum behaviour

[Haui]

Hi, it is occasionally mentioned that Autosum (Alt+=) sometimes doesn't guess the correct range to be summed.

Does anyone have further information how exactly Autosum works, like how it guesses what to sum?

A few simply examples where I struggle to understand the consistent logic of the function:
A1=1+2
A2=3+4
A3=autosum guesses correctly the cell range A1:A2

B1=SUM(A1)
B2=3+4
B3=autosum guesses 'incorrectly' only the cell A2; it appears its logic is that summing over another sum function is not what is intended

If instead B1=A1, the cell A1 is included in the autosum as in the first example, so wrapping the cell into the sum function seems to change the behaviour of autosum.

The behaviour becomes even more quirky when e.g. one empty cell/rows is included above the autosum,

E.g.:
A1=1+2
A2=3+4
A3 = blank
A4=autosum range A1:A3

B1=A1
B2=3+4
B3 = blank
B4 = autosum guesses the range B1:B3

variation1: if B1 is wrapped into a sum function, the autosum guess changes to the range B2:B3
variation2: if B2 is changed to SUM(3,4), the autosum guess changes to the LEFT = A4

Ultimately, I am just trying to get a better understanding of the function's working.
If anyone has a full explanation or a link for further reading that would be much appreciated.

Thanks

 

[sijpie]

Well I think you have neatly summed up (excuse the pun) which factors the autosum is taking into account. Probably there will be some other functions than SUM() which will have the same effect