Just to follow up, there’s a great thread on integration on the W506T here: https://www.hpmuseum.org/forum/thread-13968.html. The upshot is that is that the 506 uses Simpson’s, which will falls down in some use cases, especially ones with asymptotic curves, and needs the user to select more iterations manually.

In terms of trigs I tried these two: cos(1.57079632 rad) = 6.79491584e-9, which is correct to 4 decimal places. Not bad, better than older Casios, not as good as the latest Casio platforms which get at least 9 digits correct. arcsin(arccos(arctan(tan(cos(sin(9 deg)))))) = 9.0000001 which is reasonable.