[Therion] Survey Data Format - backclino

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