HP 15c - Manual (Page 226)

226 Appendix D: A Detailed Look at _
Execute _ again:
Keystrokes Display
| ¥
Run mode.
0 v 0.0000
Initial estimates.
1 1
´ v B 4.0681 The desired root.
) 4.0681 A previous estimate of the
root.
) 0.0000 Value of modified f(t) at root.
After 4.0681 seconds, the ridget is at a height of 107 ± 0.5 meters. This
solution, although different from the previous answer, is correct considering
the uncertainty of the height equation. (And this solution is found in just
under half the time of the earlier solution.)
Interpreting Results
The numbers that _ places in the X-, Y-, and Z-registers help you
evaluate the results of the search for a root of your equation.
*
Even when no
root is found, the results are still significant.
When _ finds a root of the specified
equation, the root and function values are
placed in the X- and Z-registers. A function
value of zero is the expected result.
However, a nonzero function value is also
acceptable because it indicates that the
function's graph apparently crosses the x-
axis within an infinitesimal distance from
the calculated root. In most such cases, the
function value will be relatively close to
zero.
* The number in the T-register is the same number that was left in the Y-register by the final execution of
your function subroutine. Generally, this number is not of interest.