Ultra Scarce 1940s Glenn Colorule for Testing Color Vision dansk international which shows some wear around

which shows some wear around the edges but I think suits it perfectly

Craven (there is some debate about it from what I've read

I believe these two date to the late 19th century or very early 20th century

please just email me and I'll give you an individual price

Ultra Scarce 1940s Glenn Colorule for Testing Color Vision dansk international which shows some wear aroundI have found a bunch of academic papers and studies discussing the use of the Glenn Colorule, but can't find even a picture of another out there anywhere. There are records of in a few academic libraries, so I know it was produced by s explained on the box text, it was made to be used to test the color vision of observers, to test the quality of light sources, and or to demonstrate disagreement caused by "pseudo," or false, color matches. There's a