NavList:

This explanation of the USN ball recording sextant appeared in Undersea Warfare magazine:

The invention of the ball recording sextant. It is ironic, and perhaps fitting, that the final form of the sextant – an instrument for measuring angular distances used especially in navigation to observe altitudes of celestial bodies (as in ascertaining latitude and longitude) – was not a sextant at all but a much earlier ancestor, the true quadrant. Developed for use at night when no horizon was visible, the recording “sextant” used no reflecting mirror. Rather, the celestial object was viewed directly as with the true quadrant. Instead of using a plumb bob, a liquid-damped steel ball recorded the altitude of the object on a screen. A drum micrometer was used to determine the precise altitude reading.

Because of its size, ease of use, and nighttime capability, the recording sextant found favor with airplane navigators, leading to “aircraft sextants” built on the same principle. Numerous examples still exist for the collector’s choosing at relatively inexpensive prices.

http://www.ebay.com/itm/191376289472?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Have any of you used such a sextant?  How did it perform, especially at night?

JMcD