#VALUE! error

[touque]

I made a simple formula in an existing sheet that was basically "A1-B1" and dragged it down for 300 more rows. Most A column and B column cells were blank.
Issue I have is that in column C many results were blank with a dollar sign. But many gave me the #VALUE error.
If I input numbers in A and B cells it would correct but why are only some doing this? I would rather not manually input numbers to correct.

 

[Scott Huish]

My best guess is that those cells aren't actually blank, but returning an empty string, like this ""
If you don't want it to return anything if there aren't two numbers:
=IF(COUNT(A1:B1)=2,A1-B1,"")

Or if you want it to treat the "" as 0:

=N(A1)-N(B1)