Tape Sag [Was: Re: fixed points in survex]

[John Halleck]

On Sun, 9 Feb 2003, John Halleck wrote:

> Date: Sun, 09 Feb 2003 17:33:46 -0700 (MST)
> From: John Halleck <john.halleck@utah.edu>
> To: Matt Ryan <matt-lists-survex@mdryan.net>
> Cc: survex@survex.com
> Subject: Re: Tape Sag [Was: Re: fixed points in survex]
> 
> On Sun, 9 Feb 2003, Matt Ryan wrote:
> 
> > Date: Sun, 09 Feb 2003 12:25:37 +0000 (Asia/Chongqing)
> > From: Matt Ryan <matt-lists-survex@mdryan.net>
> > To: survex@survex.com
> > Subject: Tape Sag [Was: Re: fixed points in survex]
> > 
> > Perhaps I'm missing something here on tape sag, but aren't most tapes, at
> > least those intended for horizontal use, supposed to be calibrated at a
> > known tension - rather than at zero tension as you guys seem to be
> 
>   No, they read direct distance.
>   (If they were just to be read directly at a specific tension
>   the feet would be different lengths, and they aren't.)

  Let me clairify my comment.
  Yes, a constant specific tension.
  No, there is no sag correction built in.

>   The "standard" tension is to use a standard correction factior.
> 
> > suggesting.  The theory I thought being that you pull the tape to the
> > calibrated tension and read it at that.  Obviously using anything other
> > than a brand new clean tape is going to have a huge effect, as are
> > anything other than horizontal legs.  And then there's also the fact that
> > at very best people just guess the correct tension.
> 
>   True.
> 
>   But enough theory.   Go out and try it.
>   Measure a 40 foot distance with the tape on the ground, and with
>   it off the ground.  A bigger difference than some folk (with a
>   straight face) tell me that they measure to.
>   [ The easy test is to measure the corners of a building, both
>   by laying in on the sidewalk from corner to corner, and by  doing 
>   the same measurement at normal eye level.
>  
> > A nice piece of work Lev - now I've had chance to read it properly.
> 
>   I agree..  Lev's paper was one of the best reads I've seen on
>   the list in a long time.
> 
> > 
> > 200 GBP for a Disto-lite laser rangefinder apparently.  Tempting...
> > 
> > -Matt
> > 
> > -- 
> > Matthew Ryan
> > matt@mdryan.net    <-- Please note my new e-mail address
> > www.mdryan.net
> > 
> > 
> > 
> > -- 
> > Survex http://lists.survex.com/mailman/listinfo/survex
> > 
> 
> 
> 
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