Hello List

As mentioned in my post before, sometimes I need to do a resurvey.
As the cave is an underwater cave and therefore the waterlevel can change I 
need to "correct" the depth readings.

E.g.:
The initial survey was done and the water depth at the start station was -5m at 
this time.
The resurvey was done at a different time and the water level at the same start 
station was -9m.
(to use positive numbers inside the data I use: "calibrate depth 0 -1")

initial survey:
centerline
data diving from to length compass backcompass fromdepth todepth left right up 
down
calibrate depth 0 -1
10 11 2.04 160 - 5.2 3.9 [ - -] [ - -] [ - -] [ - -]
...
endcenterline

resurvey:
centerline
data diving from to length compass backcompass fromdepth todepth left right up 
down
calibrate depth 4 -1
0 1 3.09 284 - 9.2 11.4 [ 0.2 2.6] [ 0.2 0.9] [ - -] [ 2.2 0.2]
1 2 2.92 298 - 11.4 12.5 [ 2.6 1.8] [ 0.9 1.3] [ - 1.1] [ 0.2 1.1]
2 3 1.96 259 - 12.5 13.7 [ 1.8 1.2] [ 1.3 1.2] [ 1.1 1.2] [ 1.1 0.0]
...
endcenterline

Station 10 from the initial survey is identical to station 0 from resurvey and 
I do connect these using equate command.
Due to the different waterlevel there is a difference of 4.0m in depth readings.
To correct this I used "calibrate depth 4 -1" within the resurvey data.
My assumption for e.g. station 0 was: (9.2 - 4) * -1 = -5.2 (identical to 
station 10 from initial survey: (5.2 - 0) * -1 = -5.2)
(as discribed in the therion book on page 19: measured value = (read value - 
zero error) * scale)

But doing so I get an error from the compiler:
therion 6.0.0 (2021-07-13)
- using Proj 5.1.0, compiled against 5.1.0
initialization file: C:\Program Files (x86)\Therion/therion.ini
reading ... done
configuration file: thconfig-survey.thc
reading ... done
reading source files ... done
preprocessing database ... done
C:\Program Files (x86)\Therion\therion.exe: error -- test.th [64] -- length 
reading is less than change in depth
writing xtherion file ... done

Line 64 is station 2 from resurvey. Depth difference is 13,7-12,5=1,2 and 
Distance is 1,96 (1,96 > 1,2).
I don't understand this error.
When changing "calibrate depth 4 -1" to "calibrate depth 0 -1" in the resurvey
there is no error compiling the data. But the depth readings are not correct 
then.

What do I get wrong with calibrate command?

Torsten
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