How can I make a calculation field empty or bland until the equation is complete. A-B=C

Say A=1 and i have not yet entered B I don't want C to equal -1.

So I want C to display only once both A and B have Data.

Thank you

How can I make a calculation field empty or bland until the equation is complete. A-B=C

Say A=1 and i have not yet entered B I don't want C to equal -1.

So I want C to display only once both A and B have Data.

Thank you

Hi,

C = If ( isempty(A) or Isempty(B); GetAsNumber(""); A-B )