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> Bill wrote,
>
>> These are a combination of the LARGEST on and off
>> figures in each set, not an average or pairing.
>> The average is almost
>> always below the 4SD figure by 0.2' or more.
>
> Sorry, but I still don't understand your concern.
> Within 0.2' of the correct 4SD is perfect.
>
> (The measurement is good if you are within 0.4'
> of tabulated 2SD).

Understood, it is the bias in that and other observations that concerns me.
Lunars under, natural and artificial horizon observations under, Not by too
much, 0.2' to 0.4', but there sees to be some systematic personal error.  IE
checks with sun  0.5' higher than of IE checks with linear targets (horizon,
distant tree line, building roof, radio tower, smoke stack etc.) Bowditch
T15 & T16 observations put me too close 100% of the time.  Both that and the
sun IE checks may indicate that my eye may be enlarging the objects along
the vertical axis, so I am not matching what a perfect eye would see through
the scope.  With point sources (star to star) things seem to be fine.  I
feel the need need to correct for that if it is fact.  0.5' between sun and
horizon IE's is, I think, a big deal.
>
> The expression "0.2' or more" I just do not understand.
> How much more?

The last round my 4SD's were under by 0.3, 0.3, 0.2 and 0.2.  By "more" I
mean off by greater than 0.2', in my case under.

 > I understand when you say that your numbers seem biased
> to one side. But if the bias in the 4SD is 0.2'
> there is no reason of concern.
> If the bias is 0.6' there are some reasons.

I would expect that I should be on both sides of the target value if all
systems were correct.  It should be a normal distribution?

> If the bias is at most 0.4' in 80 % of all observations,
> it is still OK on my opinion.
>
> Or let me put it in another way: how many observations you
> have to reject by the "0.4 test"? More than 1/2 or less than 1/2?

Less than 1/2.  After the first few months, I do not recall having to reject
any 4SD.  Doesn't mean I didn't, just that I don't recall it ;-)
>
> Alex.


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