HP 42S, DM 42 Integral

[Thomas Okken]

The fact that the actual integral is zero is causing the problem. INTEG waits for the relative error to drop below ACC, but when the true result is zero, the approximated result keeps getting smaller at the same rate as the absolute error estimate, and so the relative error doesn't get better. After a certain number of iterations, it just gives up, but since each iteration takes twice as long as the last one, the total number of times the function has to be evaluated gets large rather quickly.

In Free42, you won't notice this because it usually runs on hardware that is so fast that even evaluating the function tens of thousands of times only takes a moment, but on the DM42 this does become noticeable. Clearly the HP-42S has a more aggressive termination condition for cases like this.