Hi List

I'm using this data lines for survey:
data normal from to left right up down tape compass backcompass clino backclino

In general all data is available, but in some point I have some missing data like LRUD, Compass/Backcompass or Clino/Backclino.
When I have missing LRUD data or missing backcompass I put in  a minus "-" and this is OK.
But when I use "-" for backclino I get an compilation error:

reading source files ...
C:\Program Files (x86)\Therion\therion.exe: error -- ....filename.... -- invalid backwards gradient reading -- -
writing xtherion file ... done

Is this a bug? Because for LRUD and Backcompass minus sign  is working fine.
What sign can I use for missing backclino readings?

regards,
Torsten