NavList:

Clocks like this used to be fairly common in astronomical observatories and similar institutions. Common? Yes, if you know a synonym. The quantity referred to in the clerical jargon of celestial navigation as LHA Aries was (is) known to astronomers as Sidereal Time, more specifically Local Sidereal Time. In an observatory setting, in the days before software and apps, a Sidereal Time clock like this was a handy tool. It tells you what stars are overhead. Every navigator knows (and every observation-focused astronomer, especially amateur astronomer) knows that the observer's latitude is identical to the declination of the zenith. In addition, for the perpendicular dimension, observation-focused astronomers also know that the RA (right ascension) of the zenith is the Local Sidereal Time. If you have them both, your latitude and your local sidereal time, you then know exactly which star is at your zenith at that moment. The clock tells you —literally— what's up. :)

Would you want a clock like this that reads LHA Aries for celestial navigation? Don't get me wrong, this particular clock has an important impractical function: look gorgeous and make people think. But would you want one for practical celestial navigation? Seems like it would be nice. It would save a little calculation, right? For navigation study and training, a clock reading LHA Aries could have some practical use, but it's called LHA Aries for a reason: it's local, unique to your longitude. To use it in practical navigation, you would need to reset it based on your longitude offset from some fiducial meridian of longitude. If your homeport is Honolulu, Hawaii, for example, then as you sail east towards California, you would adjust the clock by one minute of time for every 15 minutes of arc of longitude change. When it's 23:30 Sidereal Time in Honolulu, it's 02:00 Sid.T nearing San Diego. That would be problematic! So maybe we pick a longitude as our standard and just stick with it! Set that LHA Aries to show the time at Greenwich. Then L becomes G, and a clock displaying GHA Aries would have some practical value. You read it, and then you add or subtract your DR longitude. And now you know "what's up". 

Frank Reed