Macworld Ever felt like you understood something in class or a lecture only to come home and realize you actually don’t get ...

In particular, a digit going from 9 to 0 would advance the next wheel by one step ... a binary calculator using marbles. From De progressione Dyadica: This [binary] calculus could be implemented ...

or MATH 2000 (brief calculus). The TI-83 (not Plus), TI-86, TI-92 and the TI-92 Plus are no longer manufactured. Certainly these older calculators may still be used in courses allowing any calculator.