Dear Friend,

To begin with, you have posted to the wrong newsgroup! This is an Access NG,
not an Excel one.

Anyway, the most likely explanation is that the numbers in the cells have a
decimal part which you don't see because the cells are formatted to hide it,
so they are rounded to the closest integer. For instance, if the real
numbers are 194.6, 152.6, 15.6 then the sum is 362.8, which - rounded to the
closest integer - is shown as 363. To verify that this is indeed your
situation, select the three input cells and the sum cell and change the
formatting to display a few decimals.

HTH,
Nikos