NavList:

On Jul 11, 2006, at 12:41 AM, Bill wrote:

>> Fred wrote:
>>
>> Third, have you tried changing the position of tangency to try to at
>> least get the SDs to agree?
>
> "Tangent" is by definition "tangent."  It is not, nearly touching.  
> It is
> not overlapping.  It is tangent.  Can I fudge my observations to 
> make them
> agree with 4 SD? Sure.  What is the point?  Better to nail it 
> mathematically
> and adjust than try to judge "nearly tangent" by eye IMHO.
>
> While on the subject of matching published 4SD exactly, I find that 
> foolish.
> SD 15.8" one day, 15.9' the next.  4SD jumps from 63.2' to 63.6' in 
> one day?
> Really?  No, not really.  It's at a rounding point, so SD is closer to
> 15.85'.  And 4SD closer to 63.4'.  In my case, it was pretty near 
> the 15.8'
> midpoint, so that was what I used.  Even with +/- 0.1 precision and 
> accuracy
> (instrument and observer combined) and two observations (one on the 
> arc and
> one off the arc) 0.2' off 4SD is asking a lot in my opinion.

Bill,

This is the one area where I would disagree with your responses.  
It's a judgement when tangency is achieved.  When I started out, my 
SDs were always too large.  It took me awhile to get results that 
agreed with the NA.  I was suggesting that if you could shrink your 
assessment of tangency a bit (about 0.1' of arc I believe), that 
might alter your results.

Fred

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