next up previous
Next: Data Up: Flash observations of Previous: Description of observations

Timing method

I will make a few comments about my timing procedure. I try to reset the stopwatch part of my wristwatch, a Casio Digi Graph 100M [828] DGW-30, about 4 seconds prior to an even hour UT. E.g., I might try to reset it at 015956.0. This means that if I want to find an object at a particular skymark at particular time, I can look at the stopwatch until it shows the appropriate time, ignoring any multiples of 2 hrs, and then have 4 seconds to lift my binoculars to the appropriate place. I make no attempt to set it precisely, nor do I fret as it drifts a bit while I am waiting for my cloud filter to kick in. Presently, it slews about .70 seconds per day.

I make whatever timings of events I can (the watch stores the first 29 splits plus the last split) and then take additional splits while listening to WWV or USNO telephone time. In the morning, typically, I wait until WWV 15 MHz starts getting thru fairly well. Then I wait until the beginning of the long tone at the beginning of the next minute. This split usually reads about .2 or .25 seconds greater than the actual offset. I can confirm this, more or less, from the 60-component LCD display which lights progressively each second, but which is not calibrated well enough to get me to use it in preference to the splits. I now have the offset, typically, to within about .1 or .2 seconds. I then take an additional split attempting to match the beep from the watch to the tick from the time source. This gives me the hundredths of seconds. Since I am a perfectionist I then take additional splits to try to get a better audio match. I seldom change the first one by more than .02 seconds. For some reason, the later splits seem to be more scattered than the first, as if some sort of fatigue were setting in.

I then adjust the offset to account for the .7s per day slew of the watch. This adjusted offset is then subtracted from the recorded splits to obtain the UTC which I then report. The slew adjustment varies from time to time as the crystal in the watch ages, running faster and faster with time, but this process is very slow in the early decades after manufacture of the crystal (and maybe later, I don't know).

The slew adjustment is built into the little program I use to generate the DRA format from the raw data. This program, of which I have written before, accepts an abbreviated list of the split times, which I have first written on paper while in recall mode on the stopwatch, the offset measured as above, and the date. It then directly generates the DRA output which I have reproduced in many messages here and show in the next message. After I prepare the data for the program, I verify that it corresponds to the written splits, etc. After running the program, I double check the written splits one more time against the DRA output.

If you live in the DC area and can make a local call to USNO time at 202-653-1800, you can count on a short-delay connection, making a useful reference for all manual timing work. If you live in the Ft. Collins area, similar comments apply to WWV at 303-499-7111. If you use a long-distance connection, the delay may be longer, possibly several tenths of a second. Local telephone time in the US is truly horrible, possibly off by more than a minute, and more typically oscillating back-and-forth by up to 6 seconds either way with the electric power grid. AT&T guarantees a short-delay connection to 1-900-410-TIME at USNO. WWV 2.5, 5, 10, 15 and 20 MHz are useful, as well as the various other national time services. People in the northeastern US often use CHU.



next up previous
Next: Data Up: Flash observations of Previous: Description of observations



bdp@mpe-garching.mpg.de