Tutoring math, you come to appreciate calculators. The tutor points out an interesting feature on the Casio fx-991ES PLUS C.

Typically, the log key on a calculator means “base 10 log”, aka “common log.” What about base 7 log, for instance?

The Casio fx-991ES PLUS C has a log_□□ key which can accept an input for the base.

Example: On the Casio fx-991ES PLUS C, evaluate log₇62.

Solution:

1. Press the log_□□ key, second down on the right.
2. Press 7, then arrow over once, then key 62, then arrow out of the brackets.
3. Press =

Everyone not blessed with the Casio fx-991ES PLUS C can just enter log62/log7 =

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.