"Nick" wrote...
OK good spot, the formula should have read =SUMIF(A1:A3,C1,B1:B3)
with the entry <"" in cell C1.

You are then summing values in B1:B3 where values in A1:A3 are not blank ie
they contain something even if it is a space.

That works.
....

That does not work, and you seem not to have tested it last time or this
time.

In a new worksheet, leave A1 blank, enter ="" in A2 and ="""""" in A3, and
enter {1;10;100} in B1:B3. Enter <"" in C1 and your formula in D1. What
does it return? On my system it returns 11, the sum of B1 and B2, which
correspond to the cells A1 and A2, which appear blank/empty.

Change C1 to < and D1 returns 110, which reflects the nasty truth that
SUMIF doesn't handle zero length strings as most people expect it should.