A SIMPLE CLOCK DISPLAY for the HP28C
                      ====================================

Here is a simple way of keeping and displaying  real  time  on  the HP28C.  This
code was adapted from several sources: 

<< #123E SYSEVAL 8192 / >> 'TIME' STO
<< HMS> 3600 * TIME B>R - 'TD' STO >> 'CS' STO
<< 4  FIX  DO  TIME  B>R  TD  +  3600 / 24 MOD >HMS 1 DISP UNTIL KEY END DROP >>
'CLOCK' STO

1.  Enter the current time in HH.MMSS (24 hour) format into the command line. 
2.  Press CS in the USER menu ("Clock Set")
3.  Press CLOCK in USER  menu to show the time in HH.MMSS 24 hour format in line
1 of the display
4.  Press CLOCK any time thereafter for the displayed time

The  routine 'TIME' recalls one 8192nd of the system clock, which is used in the
'CS' routine to generate  the  variable  TD  ("time  difference")  which  is the
constant offset between entered time and system clock time.  The routine 'CLOCK'
recalls, converts and formats the clock to real time. 



                            A Simple HP28C Stopwatch
                            ========================

Here  is  a  simple  stopwatch for the HP28C which uses the system clock to time
events  with  accuracy  displayed to thousandths of a second.  A 'RESET'  button
sets the timer  to  zero  while 'STRT' begins the timer.  Then, pressing 'SPLIT'
places a time split onto the stack.  'STRT'  will  restart  the  timer  at  this
point.  Time is displayed in HH.MMSSsss format. 

<< #123E SYSEVAL B>R 8.192 / >> 'TM' STO
<< 1 SF 0 'RT' STO >> 'RESET' STO
<< TM 'OFFST' STO 1 CF >> 'STRT' STO
<< 7 FIX IF 1 FS? THEN RT ELSE TM OFFST - RT + END 3600000 / >HMS >> 'SPLIT' STO
<< 7 FIX IF 1 FS? THEN RT  ELSE  1 SF TM OFFST - RT + DUP 'RT' STO END 3600000 /
>HMS >> 'STOP' STO

Variables Used: 
     TM - current time in thousandths of a second
     RT - runing time
     OFFST - offset from system clock
     FLAG 1 also used

Note:  you may wish to use the ORDER function to arrange that the main functions
RESET, STRT, SPLIT and STOP are first across the top row of user keys: 

     { RESET STRT SPLIT STOP } ORDER

Jake Schwartz,
135 Saxby Terrace,
Cherry Hill, NJ 08003, USA
[609-751-1310 home]
[609-866-6269 work]

Notes  added  by Mark Cracknell, 6 Stratton  Mews,  Of  South  Street,  Leighton
Buzzard, Bedfordshire LU7 8NT, England.  [Home :  0525-383265]
1. The code shown above contains two changes from the original - one a simple
   error and the other a functional enhancement:
   a. The original of 'CLOCK' had the sequence '/ 86400 MOD'; I have altered
      that to '/ 24 MOD'.
   b. The original of 'SPLIT' had no display setting so if you made use of
      'SPLIT' before making use of 'STOP' you might not get a meaningful
      display - I therefore taken the liberty of inserting the sequence
      '7 FIX' before 'IF 1 FS? THEN ...' in 'SPLIT'.
2. I would also recommend making the the following enhancements :-
   a. Change the '7 FIX' sequences to '5 FIX'  in 'SPLIT' and 'STOP'
      for an 'easier to use' output.
   b. Insert the sequence '"       " SWAP >STR + between >HMS and
      1 DISP UNTIL ... in 'CLOCK'.