Old GC Electronics drug store tube tester

Recently, I bought this old GC Electronics model 36-500 drug store tube tester (I don't know why!). No manual or setup guide came with it and I can't find any info on it at all. It doesn't have many tube sockets on it like most of the old corner store testers did. It has one octal, one locktal, one 7-pin mini and one 9-pin mini along with a special tester socket for 0Z4. It also has a battery tester and a tester for the old vibrators, 4-pin and 3-pin types. It has only 3 setup switches--filament voltage, 11-position selector and 0-100 load adjust. I'll try to post a picture soon. Any help or suggestions would me most appreciated.