HP 15c - Manual (Page 202)

202 Section 14: Numerical Integration
If the uncertainty of an approximation is larger than what you choose to
tolerate, you can decrease it by specifying a greater number of digits in the
display format and repeating the approximation.
*
Whenever you want to repeat an approximation, you don't need to key the
limits of integration back into the X- and Y-registers. After an integral is
calculated, not only are the approximation and its uncertainty placed in the
X- and Y-registers, but in addition the upper limit of integration is placed in
the Z-register, and the lower limit is placed in the T-register. To return the
limits to the X- and Y-registers for calculating an integral again, simply
press ) ).
Example: For the integral in the expression for J
1
(l), you want an answer
accurate to four decimal places instead of only two.
Keystrokes Display
´ i 4 1.8826 -03 Set display format to i 4.
)) 3.1416 00 Roll down stack until upper
limit appears in X-register.
´f 1 1.3825 00 Integral approximated in
i4.
®
1.7091 -05 Uncertainty of i
4 approximation.
The uncertainty indicates that this approximation is accurate to at least four
decimal places. Note that the uncertainty of the i 4 approximation is
about one-hundredth as large as the uncertainty of the i 2
approximation. In general, the uncertainty of any f approximation
decreases by about a factor of 10 for each additional digit specified in the
display format.
*
Provided that f(x) is still calculated accurately to the number of digits shown in the display.