[Therion] vthreshold

[Bruce]

>Orientating to the passage has always been most logical to me, but I do 
>see that the above is very valid. However what do you do on a true 
>vertical, as it does not have a compass bearing?

I just adopt a compass bearing to suit the general trend of the preceding
passage or to suit the orientation of the passage shape for the basis of the
LRUD.
Regardless of the compass bearing, the survey leg will still be vertical.
In truth it is academic for me now, as mostly I use a disto and pda, so no
more LRUD.  Still for all my old data...
Bruce