Multiple readings from one but not all instruments

[Andrew Atkinson]

In the ukcaving thread

https://ukcaving.com/board/index.php?threads/therion-for-divers.30044/

It has been brought up that people are taking two compass readings per
leg and also two depths for each station (the stations depths been taken
on the way in and the way out.)

This has got me thinking, the original SAP only did compass and clino,
so it would have been reasonable to take more than one shot with that
but only have one tape reading.

So Survex was kindly updated by Olly to not count multiple legs as loops
of the distoX, hopefully it would not be that difficult to amend that to
be able to miss out a reading. eg

data normal from to tape compass clino

1	2	3.22	178	-3
1	2	-	179	-4

It would seem reasonable to accept this type of grouping so long as one
of the group was a valid leg, guess it would also be reasonable to
expect the first one to be valid. This notation would show that tape was
only read once, conveying some information about reliability, maybe one
day that can be used.

There would be a question about the use of more than one instrument, say
2 compasses, especially if they had different calibration amount. People
are doing this, although it is not stated in the above thread, I expect
the dual compass readings come from the Nemo and another compass. If
this is a standard dive compass, taking the average is probably the
wrong thing to do as most are hard to read better than 5°. Maybe a data
format along the lines of

data normal from to tape compass[1] compass[2] clino

would be useful, then the sd of compass[1] and compass[2] could be set
to the respective levels

The depths on the way in and way out is slightly different sort of like
another traverse, but without the full information. Maybe this is the
same solution as what was proposed for the water level at different ends
of sumps, we do need to be able to connect stations without the full
information.

Andrew