What is the minimum recommended distance away from an edge that an inspector should take a measurement with a dial-type magnetic pull-off Dry Film Thickness (DFT) gauge?

What is the minimum recommended distance away from an edge that an inspector should take a measurement with a dial-type magnetic pull-off Dry Film Thickness (DFT) gauge?
A . 1 cm (.39 inch)
B . 2.5 cm (1 inch)
C . 6.35 cm (2.5 inch)
D . 2.5 millimeters (.10 inch)

Answer: B