I have several Master IIs, and some are still accurate enough for regular use. Aside from selenium cell deterioration, the most common problem may be imbalance of the armature. To check for this, cover the cell and rotate the meter with its dial in a vertical plane. The needle should remain on zero. If it moves as you rotate the meter, the armature is unbalanced. I've used meters with this problem by holding the meter so the imbalance is nulled out. If the needle remains steady but off of the zero point, that can be corrected by a screw on the back of the meter. Norwood and GE also made selenium cell meters that I find still useful.