There was this.
![In a world before GPS 1996669-0](https://www.eevblog.com/forum/index.php?action=dlattach;topic=413188.0;attach=1996672;image)
This is what passed for the best oscillator before GPS, and even surpassing quartz. I just restored this 1895 marine chronometer and thought it might make a topic of interest.
While I have customers send me only the brass cased instrument, they were housed in exquisite boxes of mahogany (real) or rosewood.
To obtain best precision, they were mounted in gimbals to keep them horizontal. They were wound by the same hand every day at the same time and this was reported to the ship commander under penalty of courts martial.
Greatly oversimplified, the chronometer told you the time in Greenwich England. It generally had an error rate of less than 2 seconds per day; but it was precisely two seconds per day and maintained that precision for at least three years. Then sent for service, which explains the condition after 130 years.
Your sextant told you what time it was where you were. The time difference told you how far around the globe you were from Greenwich (1 hour equals 15 degrees).
Ships, particularly military ships, carried 3. If you had one and it went out your SOL. If you had two and one went out, you did not know which to trust. With three you trust the two that behaved.
In practice, the mean for the three dial readings was used for each position shoot.
The search for the perfect oscillator drove materials science, leading to the 1922 Nobel Prize for physics for Elinvar and Invar.
The USN did not stop using mechanical chronometers until GPS was up and proven; recalling the WWII Hamilton M21 from the fleet in 1988. Quartz had been issued to three ships in WWII but the USN was never happy with it as a primary instrument because of vibration and salt. Today the Naval Academy is trying to buy them back to teach navigational skills again (EMP?)
![In a world before GPS 1996669-1](https://www.eevblog.com/forum/index.php?action=dlattach;topic=413188.0;attach=1996672;image)
![In a world before GPS 1996675-2](https://www.eevblog.com/forum/index.php?action=dlattach;topic=413188.0;attach=1996678;image)
![In a world before GPS 1996681-3](https://www.eevblog.com/forum/index.php?action=dlattach;topic=413188.0;attach=1996684;image)