I think Pentax Spotmeter III and the one in
this thread are the same.
When I peeled of the decals (I think it is the one on top of the meter), I found another decal saying something like "Pentax Spotmeter."
If the meter is in working condition, $50 is a decent price. I don't use it the meter that much, but it's very educational (and entertaining) to determine the dynamic range of the scene. My son can spend hours with it. How can you find such a fun and useful toy for a 13 yr old boy!
One of the problems with this meter (and many other old battery-operated instruments) is that it uses 1.35V mercury battery cells, which are no longer made. In this case, I have to re-calibrate it (details in the afore-mentioned thread).
I found
the manual on-line.