Allstate auto engine tester

[Mark914]

Picked up this Allstate engine tester, model 7185, vacuum / pressure gauge, compression tester , spark tester. Needs a little TLC. The spark tester seems interesting as I am I wondering how it works. My guess is 1940’s -50’s.
Was Allstate sold by Sears ?? If so what time frame ? Anyone have any literature, sales books that show this etc ?

 

[RTM]

Looks like it’s showing up in the 1951-3 catalogs, but no preview or snippet view.

The manual library at archive dot org doesn’t have it

The Manual Library : Free Texts : Free Download, Borrow and Streaming : Internet Archive