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The patent originally referred to by Hanno requires that the optical device be pendulously
suspended in the tube, such that vertical is maintained. How would he know if the device he constructed
was then plumb? This may be the reason why Hanno is now looking at spirit levels.

If the device were to be constructed by Hanno, it would need be checked by reference to some
other well understood device.  Hanno will not prove that his device is plumb by reference to
a spirit level.  That would required somehow referencing the spirit level (horizontal) to the
optical axis (vertical), a difficult task without highly accurate metal machining.  I believe
that Hanno suggested wood, an in-appropriate material for constructing this type of device.

The NavList has recommended that Hanno obtain a theodolite, which would be the standard method
of taking these meridian crossing measurements.  Once calibrated and certain, then Hanno can
compare those measurements to his device measurements and determine statistical variation.
Naturally, there will be much work in just establishing the practice of the method with
the standard device, let alone the construction and calibration of the new device to the old.

And by the way, a pendulum takes advantage of the acceleration of gravity, where the spirit
level takes advantage of the buoyancy of the bubble, with the viscosity of the fluid providing
dampening.  A spirit level is NOT a pendulum turned upside down.


Best Regards
Brad


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