I recently bought a Gossen Luna Pro from an acquaintance for $20, and yesterday I installed the Gossen silver oxide battery adapter to correct for the voltage difference. In comparing the Gossen's readings to my Nikons built in meter and my iPhone metering app, the Gossen consistently reads nearly four full stops under the other meters. (Would result in gross overexposure)
Is this meter worth repairing - is it even possible? What would you suggest?