NavList:

   

Reply

  A year ago in September 2009 we discussed using cheap digital watches 
as chronometers in the thread "How many chronometers?" I described an 
experiment I was doing using three cheap ($17.00 each) watches to 
determine how useful they would be as a chronometer. ( I have provided 
links to some of my posts in that discussion below.)

The experiment has continued now for almost a year and this is an update 
to the prior posts.

Since I had modified the test conditions temporarily to see what effect 
very cold temperatures would have on the rates of the watches, I had to 
restart the experiment on September 18, 2009, 360 days ago. The three 
watches, "A", "B", and "C" were, respectively, 7, 31 and 60 seconds fast 
at that point. I had computed their daily rates to be .1919, .3737 and 
.6263 seconds per day respectively. The watches are kept in a cabinet 
with a minimum-maximum thermometer (see photo) and the temperature range 
was 62.5� to 82.4� F ( 16.9� to 28.0 �C.)

I have checked the watches on five occasions by comparing them with the 
radio time signal from WWV and estimated the time to the nearest half 
second. Using the daily rates, I predicted what the accumulated errors 
should be and compared them with the actual error and the difference 
would have been the error if relying on the predicted errors for navigation.

The first occasion was on November 13, 2009, 56 days after the start. In 
the format for A, B, and C in seconds: actual error; predicted error; 
difference.

A = 17.0/17.7/-.7:  B = 52.0/51.9/ .1:  C = 95.0/95.1/ -.1

Averaging these differences equals -.2


December 31, 2009, 104 days:

A = 26.5/27.0/ -.5:  B = 70.0/69.9/ .1:  C = 124.0/125.1/-1.1

Averaging these differences equals -.5

March 16, 2010, 179 days:

A = 41.0/41.3/-.3:  B = 97.0/97.9/ -.9:  C = 172.5/ 172.1/ .4

Averaging these differences equals -.3

June 23, 2010, 278 days:

A = 61.5/60.3/1.2:  B = 134.0/134.9/ -.9:  C = 232.0/234.1/ -2.1

Averaging these differences equals -.6

September 13, 2010:

A = 79.0/76.1/2.9:  B = 164.0/165.5/ -1.5:  C = 281.0/285.5/ -3.5

Averaging these differences equals -.7

Evaluating this data shows that the greatest difference between 
predicted time and actual time was 3.5 seconds after 360 days which 
would result in less than one minute of longitude error in almost a 
year. So using any one of these watches as a chronometer would provide 
sufficient accuracy for celestial navigation.

Averaging the three readings resulted in a maximum difference of .7 
seconds which would provide a longitude to an accuracy of less than 
one-quarter of a minute.

So it appears that if the watches can be kept in the cabin where the 
temperature can be maintained at a comfortable temperature for the 
occupants, 17� to 28� C, that these three $17 watches are all you need 
for a year of voyaging without recourse to a radio time signal.

gl

Check out these previous posts:


http://www.fer3.com/arc/m2.aspx?i=109724&y=200909

http://www.fer3.com/arc/m2.aspx?i=109757&y=200909

http://www.fer3.com/arc/m2.aspx?i=109766&y=200909

http://www.fer3.com/arc/m2.aspx?i=109824&y=200909

http://www.fer3.com/arc/m2.aspx?i=109825&y=200909

http://www.fer3.com/arc/m2.aspx?i=109847&y=200909

http://www.fer3.com/arc/m2.aspx?i=109894&y=200909

http://www.fer3.com/arc/m2.aspx?i=109942&y=200909

   

Reply