Time out



      Turn your Spectrum into an expensive and rather

      bulky wristwatch. An interesting and carefully

         designed program that you get second hand

           from Douglas Richardson of Edinburgh.



Chapter 18 of the Spectrum manual describes two analogue

clock programs: the first version uses PAUSE as the 'hair-

spring' but, as the manual says, there is a difference of

1/50 between consecutive PAUSE numbers equivalent to half

an hour per day. By altering the PAUSE value you could

probably increase the accuracy.

  This program prints out a digital watch and, as the

result is displayed as a number, setting and synchronysing

are much easier - the PAUSE is compounded to give this

accuracy. The performance of the watch then is dependent

more on the stability of the timing delay function of the

computer, rather than the ultimate accuracy of the internal

clock.

  The PAUSE at line 110 is the main reference, it allows a

slight gain which is essential if a following PAUSE is to

be corrective.



 Calibration



With PAUSE 49 at line 10 and REMs at 135 and 153 (see set-

ting) run the watch for one hour. Seconds gained per hour

times 5/6 rounded to the nearest integer gives you the

PAUSE to be entered at line 135 in place of the REM. You

must round down if you intend to use a third PAUSE for

maximum accuracy. In the author's first check the gain was

five seconds per hour:



5 x 5/6 = 4.16667



PAUSE 4 was then used at line 135.

  If you opt for maximum precision then with PAUSEs entered

at lines 110 and 135, and a REM at line 153, run the clock

over a much greater length of time. Seconds gained per hour

x50 will give you the PAUSE value to be entered.

  Looking back to the author's example, the third PAUSE was

not necessary as the error was only two minutes per day

with one PAUSE, and 4.8 seconds per day with two PAUSEs.

However, your Spectrum may be different and require this

fine tuning.

  Subject to stability, the target accuracy should be 24/50

seconds per 24 hours. This would give you an error of one

minute per 500 days!



 Setting



For ease of setting, the seconds increment by five, but run

normally once set. Set the time with the seconds just ahead

of real time then press G when the time is correct. Date is

for effect only and may be changed at line 400.