So as it turns out, this vintage light meter that my Son bought at a thrift store is actually a Sekonic L-136 Micro Clip-On Shoe Mount Cds Reflected Lightmeter sold from 1962-70 for Leica and Canon rangefinders. Takes a #625 battery - PX625 from RadioShack should do the trick. The plastic window on top has come loose and the battery cover has corrosion on it but not too much. In 1962 this light meter sold for $22 new. My Son paid 69¢ for it last week. I found an eBay seller with one listed as "Buy It Now" for $149.99.