A response factor is a number which relates the MiniPID response to a particular VOC relative to isobutylene. If you know what VOC you are measuring then multiplying the displayed concentration by the RF of the VOC will result in the actual concentration of VOC.  Response factors values can be either inferred from the chemical structure or tested directly.

Response factors for gases are different for the MiniPID 10, 10.6 and 11.7 eV.