Concise still sells slide rules, believe it or not.
The advantage of a circular slide rule is two-fold: a longer scale length (for greater precision) packed into a smaller package, and you will never find your answer is just off the end of the scale.
Concise 600-ST Scientific Tables, 2" Circular
One of my favorite rules, and one I used to use quite a bit. Made by Concise in Japan, and resold in the U.S. by Sama & Etani, the produced several different versions, including electrical engineering, chemical engineering, metric conversion, and weights and measures conversion versions. Many companies had their own logo put on them and gave them away as promotional items. The slide rule part was the same on all of them, only the insert was different. I've also got the manual and case! Would you believe this goes for around $90?
This one belonged to a "Robert A. Boyle, 319 Sunset Ave, Rensselaer, NY 12144, 449-2367" By pure coincidence, I lived on the next street over for a while, and never realized...
Concise 28N, 3" Circular
The Concise 28N, a very common circular slide rule, is still produced today.
© 2003 W. E. Johns