[Therion] Survey without clino

[Tarquin Wilton-Jones]

> data diving from to tape compass fromdepth todepth
> 0 1 5.53 5.5 20 22 #that is a 2 metre rise in altitude
> 1 2 50 37 22 -10 #that is a 32 metre fall in altitude
> 2 3 37 100 10 -15 #that is a 25 metre fall in altitude

Of course there is also the other very cool "cylpolar" survey (just put
that word instead of "diving"), where you measure with a horizontal tape
and spirit level (to keep the tape level) and plumb line. Syntax is
identical, but the tape is held horizontally instead of diagonally.

You can see the different types of survey here, in the "DATA" section:
https://survex.com/docs/manual/datafile.htm

Just be aware that this is aimed at Survex, so it uses the "*data"
syntax, and it says you can use "-" instead of "0" for the clino if you
took no readings. You're using Therion, so you need to use "data", and "0".

You might be interested in "depthchange" for example, which allows you
to specify a single relative depth change instead of two absolute depths.

This should have the effect of flipping positive to negative in dive data:
calibrate depth 0 -1

Aside: changing the "zero error" (the first number) to a number will
cause that any metres to be subtracted from each relative depth change.
So positive depth changes are reduced, and *negative ones are
increased*. I cannot see any use for that feature even in actual dive
data, or cylpolar data, so in general it probably should be left at 0.
Scale is the only thing that really makes sense.