HP 35s Scientific Calculator - Manual (Page 345)

More about Integration E-9
Because the calculation time depends on how soon a certain density of sample
points is achieved in the region where the function is interesting, the calculation of
the integral of any function will be prolonged if the interval of integration includes
mostly regions where the function is not interesting. Fortunately, if you must calculate
such an integral, you can modify the problem so that the calculation time is
considerably reduced. Two such techniques are subdividing the interval of
integration and transformation of variables. These methods enable you to change
the function or the limits of integration so that the integrand is better behaved over
the interval(s) of integration.