[Leica] plastic verses metal (sextants)

["Alan Hull" <hull@telia.com>]

Luggers
   The following is from the Cruising World magazine website.  It is
about plastic verses metal sextants for astro-navigation.  Sound
familier?  Substitute photo for sights.

http://sailingworld.com/2000/06/Sextant.htm
I knew that subjectivity would play a large part in our experiment, as
it does in real life. I take better sights with an instrument I love.
The subjective factors that affected our sights included our
experience, the weight and the feel of the units, the quality, size and
colors of the filters, the orientation of the index lever, the feel of
the micrometer drum as well as fatigue, impatience, nervousness,
sleepiness, or whatever emotional or physical state we were in that
day.

I’d have to stand by my disparagement of the plastic sextants. My
experience and distant memories of physics classes tell me that
different thicknesses of plastic will heat and expand at different
rates. That plastics are affected more quickly by heat than metal I
would take to be a given

As for the inertial properties of various weights of sextants, there
was this guy named Newton who mentioned that an object at rest tends to
remain so. I have found that a lighter object will be easier to start
moving than the heavier and therefore more difficult to hold steady so
I’ll stand by my preference for a heavier sextant in a seaway when the
boat is leaping around.