When building spreadsheets, I often SUM() up large sets of numbers in Excel. However, a common problem arises when you want to write --- or N/A to signify that a cell is intentionally empty. This causes SUM() to error.

Fortunately, there's a simple solution. First, replace your --- or N/A with #N/A. Then, replace your SUM(A1:A10) with

SUMIF(A1:A10,"<>#N/A")

where A1:A10 is the range of cells you are summing.