fixed points in survex

[Lev Bishop]

On Thu, 6 Feb 2003, John Halleck wrote:

> I personally think that the "clean tape" sag correction on the other
> hand would be a lot closer to reality on a dirty tape than the 
> totally uncorrected values being used now.

One way you could do a better sag correction is if you took 2 separate 
tape measurements, with 2 different tensions in the tape. You'd need some 
kind of tensioning device (I'm thinking of a spring-loaded puller thing 
the tape end man can use - should be pretty low-tech and reliable). With 
the two measurements you could correct for tape stretch and sag quite 
easily and even remove "dirty tape" effects to first order. Nice in theory 
but I can't imagine anyone doing it - cave surveying is painful enough as 
it is without needing even more numbers to be recorded. If you really care 
that much about accuracy in your length measurements its probably a better 
idea to buy a laser rangefinder now that they're somewhat affordable.

Lev