NavList:

   

Reply

I've got a Mark III.  It's much harder to adjust than a sextant with a
drum.  It doesn't have a magnifier, which makes it harder to judge
contact, and is difficult to set.  It's horizon mirror is also split,
so it's tough to bring images into contact: there's no overlap of the
reflected and straight images as with a half-silvered horizon mirror.
You need to use the vernier to read to the nearest arcminute (or
possibly to the nearest 5 or 10 arcminutes).  So you can't just read
the minutes off the dial.  You can't read below an arcminute (or
perhaps 5 or 10 arcminutes).

The index arm is so sticky that it's tough to nudge it except in one
direction, which is what I meant in the previous paragraph when I said
it is difficult to set.  A difference in reading depending upon the
direction of adjustment may occur due to slop in the pivot bearing.
Never tried to measure that.

On Sep 16, 2005, at 10:00 PM, Herbert Prinz wrote:

> The Davis Mark 3 has a Vernier scale. I don't understand why it should
> make a difference wich way you move the index arm before reading. This
> is only a concern with micrometer drums.
>
> Herbert Prinz
>
>
>
> Espen S. Ore wrote:
>
>> Given the way the Davis Mk. III works I believe it is
>> difficult to come any closer than 1-2", and that yes, one should move
>> the arm in the same direction for all the shots.
>

   

Reply