A Calculator with an Unadvertised Digital Clock A new useage of an established laboratory tool has come to our attention. One of the scientific calculators on the market today' has, as advertised by its manufacturer, a digital clock-the Hewlett-Packard HP-55. However, another of the Hewlett-Packard calculators, the HP-45, contains an unadvertised clock. The operation of the clock is as follows: 1)To access theclock, push the RCL key followed by simultaneously pushing the CHS, the 7 and the 8 keys. The simultaneity is important and i t may take the user more than one try to do i t correctly. The user may easily recognize success as the display will change to 00.00 00 00.2) The clock is started and stopped by pushing the CHS key. 3) The CLX key will clear the counter. The counter may be cleared whether or not the clock is stopped. 4) Alternate kevine . ..of the EEX button removes and restores the tenths and hundredths counters. 5) While the counter is running, internard~ntrdljpla)c may he ztored in 10 memory I C ~ I S I P ~hy S pushing the U-Y keys $11is not nwcssorv to push theS'~'O 1.1). I 'I'he stored rpsults mas he rrealled after the counter is "topped by vushlng the HCI. key t'ollowed hy the number of thedeslred rrgister.Thedi.plily mnnot herturtcl when the counter isnot running. 6)pushing the FVl'KR key restores the calculator to the ealeulational mode. The calculator clack time equals 0.8847 real time.2 Thus there about 53 min 4 sec t o the calculator hour. Multiplying results bv the reeimoeal of the above factor gives quite accurate results. The major usefulness is the ability tostore ten intermediate times. An experimenter merely need record whieh register corresponds to whieh observation and a t the conclusion of the timing of the experiment can access the times of the various events.
' Karp, S., J. CHEM. EDUC., 50, A346, A373, (1975). Measured with a standard deviation of 6 X Simon Salama a n d Doren Indritz Princeton University Princeton, New Jersey 08540
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Eugene E. Wells, Jr. Naval Research Laboratory Washington. D.C. 20375
Volume 53, Number 6,June 1976 / 385
