Correct me if I'm wrong but isn't the L308 normally an incident meter. Does it have the integrating sphere? How were you using it for shadows and the zone system?
You could always compare it to the Sunny 16 rule. Take it out in the sun, set the ASA to some known value and see if the reading comes out 1/ASA at f/16. It would be hard not to see 2 stops of error.