NOS ('70's) OLSON UHF Varactor Tuner with Data Sheet

Description

For sale is a vintage OLSON Model XM-676 Varactor UHF Tuner, left behind in my late father's electronics inventory, which was stored in a smoke-free home.  My father was an active HAM radio operator for over 70 years, and was a radio and other electronics serviceman for much of his life.   He always kept a generous inventory of new and used parts on hand for speedy repairs for his customers, available for walk-in customers to his radio shop, and handy for his own electronics projects.
I have generally found good information on the components that Dad left behind, but I've not found too much on this one.  I found this tuner advertised in a 1978 Popular Electronics catalog on line, which only said "UHF Varactor Tuner with Data Sheet," and no further information, I guess assuming that electronics buffs already knew what this was.   Hopefully you can see what this is and how it works from the photos, though the plastic makes it somewhat hard to see.  I am reluctant, however, to remove it from the brand new packaging.
See if this is something that you would like to keep on hand in YOUR vintage electronics inventory!!
Thanks for looking here!
(misc 22)