David, I have the same meter and have been using it for at least 7 years, maybe more. When calibrating it, the copper plate goes on the bottom with the copper facing up, then the plexiglas goes on top of that. First set the zero adjust screw to zero the meter, which is under the left white plastic removable plug. Then remove white plastic removeable plug and place the meter on top of the plexiglas. Adjust the meter to read 14%, then repeat the process (adjust to zero and then adjust to 14 %) until they both remain constant. You need a very small straight blade screwdriver to do this. Hope that is clear.