Hot Rods Pennzoil Kontax System box question?

Hi, I have an unusual item that I picked up and have no info, nor can I find any info on.....This is a wood box with latch that has a decal that states "Pennzoil Kontax Systems"....Any clue as to what it's use was, and age?....Thank you for any help, in advance.

 

Service stations & repair shops using Pennzoil products kept records of service performed on customer vehicles. When service became due on the rig, shop bookkeeper or foreman shoots a penny postcard to customer to remind them to bring it in ...
Later versions are found in steel file form ...

 

So this would be dated around the 1930's?

 

......................................More likely late 40's-early 50's.

 

https://trademarks.justia.com/715/56/pennzoil-kontax-system-71556911.html