Longest computation that your calculator performed for you?

[Gerson W. Barbosa]

89235.7408 seconds or 24h 47m 15.7s to compute \(\pi\) to 707 decimal places on an HP 50g. Most of this time, probably more than 90%, due to the slow processing of long algebraic expression in exact mode, though.

http://www.hpmuseum.org/forum/thread-7939.html