HP 35s HP 35s scientific calculator - User Guide - Page 140

Accuracy of Integration Since the calculator cannot compute the value of an integral exactly, it approximates it. The accuracy of this approximation depends on the accuracy of the integrand's function itself, as calculated by your equation. This is affected by round- off error in the calculator and the accuracy of the empirical constants. Integrals of functions with certain characteristics such as spikes or very rapid oscillations might be calculated inaccurately, but the likelihood is very small. The general characteristics of functions that can cause problems, as well as techniques for dealing with them, are discussed in appendix E. Specifying Accuracy The display format's setting (FIX, SCI, ENG, or ALL) determines the precision of the integration calculation: the greater the number of digits displayed, the greater the precision of the calculated integral (and the greater the time required to calculate it). The fewer the number of digits displayed, the faster the calculation, but the calculator will presume that the function is accurate to the only number of digits specified. To specify the accuracy of the integration, set the display format so that the display shows no more than the number of digits that you consider accurate in the integrand's values. This same level of accuracy and precision will be reflected in the result of integration. If Fraction-display mode is on (flag 7 set), the accuracy is specified by the previous display format. Interpreting Accuracy After calculating the integral, the calculator places the estimated uncertainty of that integral's result in the Y-register. Press  to view the value of the uncertainty. For example, if the integral Si(2) is 1.6054 ± 0.0002, then 0.0002 is its uncertainty. 8-6 Integrating Equations