request

Ted Molczan (molczan@fox.nstn.ca)
Wed, 12 Jun 1996 10:45:23 -0400

Anthony Beresford wrote:

>2. Somebody mentioned stop watches with multiple stored
> memories. Pleas send me some detailslike brand names and costs.
>I could certainly use such a   mechanism chasing NOSSes.

Here is an excerpt from a message I sent to another
observer, that will answer your question and more:

Timing is another critical issue. I use a wristwatch with a built
in stop watch, with a 30 split time memory. (Casio Lap Memory 30,
Module 863, about $40 U.S.) Before I go out to observe, I 
start the watch against the WWV time signal, and take two or
three splits, each at 5 seconds past the minute. If the radio
reception is very clear, and I am not too tired, I can synchronize
each split to the nearest 0.01 second. The watch displays the
split for several seconds, so I can write it down. If I can
produce two or three splits in a row that are almost exactly
one minute apart, then I know that I can refer the splits I 
take in the field to the correct time. For example:


Actual WWV Time    Elapsed Time  Split
20:31:05           0              0
20:32:05           00:00:59.96    1
20:33:05           00:01:59.94    2
20:34:05           00:02:59.93    3 
20:35:05           00:03:59.93    4
20:36:05           00:04:59.93    5

So I tried to start the stopwatch at 5 seconds past 20:31. Then
I took 5 splits at one minute increments, until I achieved 3
consecutive ones that agreed to the 0.01 s resolution of
the watch. Thus I have a very accurate time base for the start
of the night's obs. In the field, I simply note the split count
beside the drawing of each obs' reference stars. I try to
leave a few unused splits at the end of the night, so I can
synchronize once more to WWV. This is necessary because the 
watch has a significant drift, or error, even over 5 or 6 hours,
which I can correct for because I have established accurate
calibrations at the start and end of my obs. That is part of
the reason for starting the stop watch and calibrating before 
making the first obs. The other reason is that if I accidentally 
stop the watch instead of taking a split, I will not lose the 
splits taken up to that point, because they have been calibrated.

One other tip. If WWV is not coming in clearly, then phone the
station (303-499-7111) and calibrate over the phone. That way
you can hear each clock tick very clearly, which greatly
improves your ability to calibrate to the nearest 0.01 s. Also,
note that I calibrate to 5 s after the minute. You might ask
why not the start of the minute. The reason is that there is
a several second gap without ticks between the announcement of
the upcoming minute and the beep that starts the minute. This
gap means makes it hard to anticipate the start of the minute,
leading to greater error. I use the ticks leading up the 5th
second tick to establish a rhythm in my trigger finger, so 
that I take the split as close to the second as possible.

As you can tell, it is quite possible to become quite fanatical
about precision, but that is essential to the task of orbit
maintenance. <end of excerpt>

Tony, one other point. If I could find a stop-watch with the
same functions as the Casio wrist-watch/stop-watch, I might
prefer it. A real stop-watch has larger buttons, with greater
travel, which provides better tactile feedback. Basically, if
you can hit the buttons more confidently, you should achieve
greater accuracy, or at least greater consistency.

I suggest looking in a professional journal for Industrial
Engineers for an advanced stop-watch, since that profession
often makes use of stop-watches in "time and motion" studies.

bye for now