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Fred Hebard  writes:

> It's more accurate to determine the index error by first touching the
> reflected lower limb to the upper limb, recording the result, then
> reversing and recording that result.  Index error is half the
> difference.  Usually three measurements on each limb is more accurate
> than one on each; measure one then the other three times.  As a check
> on your interpretation of contact, you also can calculate the sun's
> semidiameter from these measurements; it's one fourth of their sum.  It
> should be no more than 0.1 arcminutes of that recorded in the Nautical
> Almanac.

I'll do this after work today (weather forecast is promising).

> Always turn the index screw in the same direction when bringing the
> limbs into contact.  Never back off on the index screw to perfect the
> contact
>
> Only adjust the mirrors if the index error is out by more than 1 or 2
> arcminutes.  This shouldn't be necessary very often.  You don't want to
> be constantly adjusting them.

OK.  This is good to know.  I always adjusted the mirrors, which is
difficult with shades in place.

> If you use the clear glass on the horizon, you can leave the same
> shades in place.

I guess refraction through the glass on the horizon is never a problem?
Right now I have difficulty reasoning if this could be problematic or
not.

Thanks for your help.

Asbjørn

   

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