I have very recently aquired a device called a "Flash-o-graph". Made by company called Wilcox, from the box label it is a "synchronizer and shutter tester". Does anyone know of these? Better still how to set up and use one? I have no idea if it is even complete, but phosphor inside is good.

I'm not going to get this 100% right, cuz it's been a long time since I've played with one, but GE made the same thing and in the early days you loaded the drum with bromide (enlarging speed) paper. Later on they used phosphrous.

Some how you have to get light behind the lens with this thing in front. There's a slit somewhere and you spin the drum which fires the flashbulb, the light makes a streak on the phosphrous. Then you somehow have to get light that's timed by the shutter in there somehow regular light bulb behind the camera?), usually it will be a short dash. When the dash lines up with the brightest part of the streak, it's timed.

I can't find my copy of "Synchroflash Photography" by Morgan and Lester but there's a pretty good description of it in there, and that was printed in '39 before the Anny and the golden age of flash bulbs.