Backsights

[John Halleck]

On Sun, 19 Jan 2003, Hazel Barton wrote:

> Date: Sun, 19 Jan 2003 10:11:24 -0700
> From: Hazel Barton <hazel@hazelsbugs.com>
> To: cave-surveying@survex.com
> Subject: Backsights
> 
> I agree with Pat, that it's important to write down uncorrected backsights
> and then do the math in your head to esure on-site accuracy of the survey.

  It the face of magnetic anomolies, a survey with uncorrected fore- and
  backsights can be salvaged.  (Particularly in the presence of loops.)
  I've had articles in several places on how to do this in the case
  of loops.
  If they are "CORRECTED" (or averaged) before being written down you
  have junk data.
  
> There is another trick I do when I'm sketching, I usually sit close to one
> of the instrument readers while they're getting the shot. That way, they
> don't have to yell the numbers out for the whole world to hear. As a result,
> the person reading the reciprocal instrument is less likely to 'cheat' -
> that is, remember what the fore-sight was, and try to get that number on the
> backsight.

  Bravo!

> I've been horribly guilty of doing this myself, when we're in a rush, it's
> pizza for dinner - and it's such a pain to try and get the reading to agree
> within a degree. Of course, these are usually my projects, so I deny
> everything!!

  For some surveys, they won't agree within a degree...  because magnetic
  north doesn't agree within a degree between stations.
 
> Hazel
> 
> 
> 
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