That does not distract, by the way, from the high value of having a good old fashioned watch on board whose rate we monitor frequently. A modern justification for learning cel nav after all is to be independent of electronics for ocean navigation, and we need to know the time to do cel nav well... or at least efficiently. Put another way, you can sail around the world fairly efficiently from port to port with nothing at all but a watch (and some books and knowledge), but take away any time piece and it will be difficult to DR for 100 miles. Our textbook Celestial Navigation has extended sections on time keeping in navigation.
Thus if you have a watch for navigation, you will need some way to check it frequently so you can establish its rate, ie how many seconds it gains or loses every week or so. A typical quartz watch is 15 to 20s/month and they are not as well temperature compensated. But we need some way to test that this is really true, so we show below here four independent ways to get accurate GMT.
In principle any one method would do, and one could just list what the methods are, but unless you see them side by side, then that would have to be taken on faith—a type of justification we try to avoid in navigation whenever possible.
Here are the methods
(1) Tune in an HF (SW) radio to one of the international frequencies that broadcast time tics. These are listed in Radio Aids to Navigation, the applicable chapter we have online at this link. The best known and most often used of these is WWV and WWVH at 5, 10, 15, 20 MHz.
(2) Call this phone number to hear the WWV broadcast on your phone: (303) 499-7111. This is a great trick, and it would seem that navigators might want to have this number in their contacts list.
(3) Logon to www.time.gov and select UTC and see the time presented for you. You will see their note that the displayed time is "Corrected for network delay."
(4) Use any GPS that is connected to satellites and giving an active location to find the display that will also show the UTC. Note that the GPS will turn on without satellite connections and indeed might even tell you the time, but this is not dependable without the actual connection.
(5) Read your cell phone time. When you are connected to a network the phone should give you the correct time. Note that strangely enough, the iPhones do not have a native display of time accurate to the second, but there are numerous free apps that read it and then show the time to the second. I should also note that i have seen rare instances when the cell phone time was off a few seconds over a period of several minutes, but I do not know what might be the source of this. The primary source of time in the phones is the network providers, which are in principle getting the time from GPS.
(6) Most modern computers are designed to show the network time whenever you are logged on to the Internet. If you are some period of time off line, then the computer could drift, but if you have a wireless connection, your computer should be showing the right time.
Here is a video showing the whole band playing at once... in keeping with our totally non-professional standards of production.
Here is an example for finding watch rate by recording watch time and correct time. First set the watch and then every few days record its error, to get a table like this one:
from this we can make a plot as shown below.
Figure 11.5-2. Chronometer log plots. Top is an inexpensive quartz watch, which is slow, showing a rate -3.5s/10d. Bottom is a $600 watch with a guaranteed rate of <10s/year (dashed lines), but actual rate was +1.1s/10d, which shows we need to check these things. Bottom data compliments of Shawn Cook.
Excerpt From: David F. Burch. “Celestial Navigation: A Complete Home Study Course, Second Edition.” iBooks screen capture.