Got this interesting "Astro Cards" lot the other day, I had not heard of them until I got them. Kind of a predecessor of nowadays common cellphone apps, but analog. Maker looks to be out of Natrona Heights, PA.
A card slips into a back-lit wood and plexiglass holder that is about 6.5" square and 3/4" thick, uses a 9v battery. Rheostat on the front varies the intensity of the red light. Cards can be easily read in the dark.
I got a TON of cards with this, really quite an interesting tool. Anyone ever used these, and what time period are they from?
Tom Duncan
PS: Hoping it is OK to post here, these are 'classic' in a sense and the forum description does say "...and observing with older scopes". Moderator, feel free to move this to a more appropriate forum as you see fit.