It was a simple piece of cardboard with 3 wheels inside of it, dial in the colors and it told you the values of resistors, capacitors, and on the backside 2 scales of inductors! (catalog number 271-1210)
While no replacement for proper education on the subject, it proved itself more than useful, so useful I still own the darn thing to this day 20 + years later, and even mention it in one of my Instructables as "the best darn piece of cardboard they don't make anymore".
The problem with it is, when radio shack changed from Archer brand stuff in brown packages to R (circle) stuff in blue and white packages, and eventually dwindled their electronic supply down to a couple of cabinets from 3 walls of the stuff, this handy device disappeared.
Without getting into too much RS / Tandy / Archer history, I would guess it had not been produced since the mid 1990's ... and thats a shame.
I have been meaning to make my own similar version of the card ever since I started Instructables, but ironically, I was going nuts trying to figure out a cardboard project for the "Gorilla Glue Cardboard Contest"...
Then one night, planning out how to shove a Cmoy amp into a 9volt battery, I was using this thing and all of a sudden all the DUH's came into place!
Welcome to my 6th Instructable.