HP 33s hp 33s_user's manual_English_E_HDPM20PIE56.pdf - Page 48

2. Reusing a number in a calculation. See appendix B for a comprehensive list of the functions that save x in the LAST X register. Correcting Mistakes with LAST X Wrong One-Number Function If you execute the wrong one-number function, use {  to retrieve the number so you can execute the correct function. (Press ‡ first if you want to clear the incorrect result from the stack.) Since Q and | T don't cause the stack to drop, you can recover from these functions in the same manner as from one-number functions. Example: Suppose that you had just computed ln 4.7839 × (3.879 × 105) and wanted to find its square root, but pressed  by mistake. You don't have to start over! To find the correct result, press { #. Mistakes with Two-number Functions If you make a mistake with a two-number operation, (›, …, z, q, , { F, | D Qor | T), you can correct it by using {  and the inverse of the two-number function. 1. Press {  to recover the second number (x just before the operation). 2. Execute the inverse operation. This returns the number that was originally first. The second number is still in the LAST X register. Then: „ If you had used the wrong function, press {  again to restore the original stack contents. Now execute the correct function. „ If you had used the wrong second number, key in the correct one and execute the function. If you had used the wrong first number, key in the correct first number, press {  to recover the second number, and execute the function again. (Press ‡ first if you want to clear the incorrect result from the stack.) 2-8 RPN: The Automatic Memory Stack