Hand held VS in camera meters.

As I recall, the gray card isn't meant to be read straight on but at an angle to the light source or at an angle to the meter.
I should have Kodak's instructions around here.

Didn't Hicks write an article about gray cards actually being 12%?.................OH GOODY! Another twist!

I don't think I'd go adjusting anything until you're sure what's going on.