Question on Goerz Red Dot Artar 30

[Abe]

I bought a Goerz Red Dot Artar 30in. I have attached an image link below.
https://ibb.co/p4Gzscg
Does anyone know what is the scale in the background used for?
It says Roberts Photo Mechanix Inc, Goerz 30in
The person who sold it told me the lens was from a teardown of some photographic equipment.
Is the scale useful for anything ? Any opinions?
Thanks

[Daniel Stone]

It's a scale used for reproduction purposes, the original use for most Red Dot Artar lenses.

[Abe]

Thanks for letting me know. Appreciate it!