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Dear Dan,

> IF a sextant:
> 1) has a frame with an arc of 60 degrees,
> 2) can measure 120 degrees due to the double
> reflecting principle,

Because most sextants actually have somewhat more
that 60 degrees arc:-) And they are still called sextants.
Freiberger measures 125 degrees, same does (modern)
C+P. But Astra IIIb has 130 degrees
(all these data from Celestaire catalog)
and my own SNO-T has 140 degrees on the scale.
All these devices are called sextants,
though SNO is in fact closer to a pentant.

Moreover, I have a pocket Troghton and Simms "sextant"
with the arc of 150 degrees, and still everyone calls
this a "pocket sextant".

I also have an aviation bubble horizon MkIXa
"sextant" with 90 degrees exactly on the arc
(so it should be properly called an "octant")

But still everyone calls all these instruments
"sextants".

All these instruments are double reflecting, of course.


Alex.


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