In other cases, the original sensor may be defective, and a newer meter, such as KEKS meters, may be required.
Finally, some silver cameras required a mercury battery to power their original light meter. However, these mercury batteries type PX625 are not manufactured anymore, and the models which replace them type EPX625 are not quite identical. In this case the original cell is slightly wrong. It becomes necessary to use an external KEKS light meter.