Bias Calculation

I'm attempting to create a CF for bracketing standard Bias during HPLC runs, the calculation (as outlined in our SOP's) is as follows:                         
% Bias =[ |A-B| /A ] x 100
Where:                       
 A:        Mean area response of Standard prior to the samples
 B:        Mean area response of Bracketing standard after the samples

Is this field possible to create ?