How about =IF(ISERROR(F3/G3),"",F3/G3). If the calculation F3 divided by G3
returns an error, return "" to the cell containing the formula, if it doesn't
return an error, perform the calculation and return the result to the cell
containing the formula.
You'll have to be a little more specific in describing your needs. There
are many formulas and solutions similar to what you have started to
describe. Please post your formula that is of concern and what results you
would like for it to return. Then, someone will help.