I got my first one, a Sun Hemmi 6" at around 12 years age. I loved it. And even more so when I understood that the C and D scales gave twice the resolution the A and B scales did.
The more I used it, the more I understood about logarithms and trigonometric functions. The P (Pythogarean) scale was a real eye-opener. So I was well prepared when we got that far in the math classes.
It was only when the HP 35 appeared that I reluctantly let go the 12" Faber Castell 154. But I still have it.
I happened to meet a guy at the La Posada hotel in Winslow, Arizona and we had a couple of beers together. I had no idea who he was and we found out that we had a few common interests. I asked who he was. Tom Osborne, he said. The guy that started it all with his “Green Machine” - built from discrete components and using the Cordic algorithm. Do i need to say that it became a very late evening? My wife and Tom’s Paula found something else to do. I think. A great evening and a great memory.
Of course, I got myself a HP 97, with magnetic memory card and built-in printer after that.