Sittin’ in the loft where my wife works at her desk and I get distracted at mine, cleaning out the piles of things I’ve ignored for the last six months. I found this in my flight instructors office about twenty years ago. Kept it. Today I took it out of the sleeve, spun it around, and completely forgot how to use it. Rules of thumb and FMS flight computers rule my world today. I didn’t learn on this CR3 style of slide rule. I learned on the E6B. I see one of these currently for sale on Ebay for $50.
There are a lot of matchings to make it work. Put two known variables together on the outer rim, and look around the inner circles to see the answers. The speed arrow to your speed, look fro distance outside and under it is the time to travel that. Simple things. But quick and effective. In a way I miss the simple things but in no way do I really wish to live within them again.