[Therion] Gradient out of range - does not process

[Tarquin Wilton-Jones]

> Theodolites are not really set up for doing traverses, for a loop of a few hundred metres we have an mis-closure of about 1m. I would be disappointed if I was using a disto X. It seems to be par for the course. The show cave owners paid for a traverse when they where tunnelling. They claimed millimetre accuracy however were metres out. Lead to a bit of an arguement between the caver surveyors and the paid surveyors about Which direction to dig the tunnel. It was resolved when the tunnel broke through. Luckily the tunnelers listen to the cavers. 😁

Well, that saves me buying one (as if I could afford one). I was
expecting them to be super-accurate, if calibrated properly. I'm
assuming this is not a calibration issue though. Theodolite grades were
always given as being so much higher than regular surveys, so this is
quite eye-opening.

Presumably the existing "theodolite" mode you were referring to in
Survex/Therion is designed for use with separate positioning and
levelling, since levelling gives extremely high accuracy vertical
position, so all you need then is the horizontal. (This is similar to
how OS land surveys were traditionally done, with the horizontal and
vertical surveys being almost entirely unrelated, and only tied in a few
places for convenience.)

I will add a note that yes, out-of-range crazy numbers is actually
normal with theodolite-style devices. Not just for inclination.
Certainly there are some other surveys done with thodolites (both
professional and home-made) where the compass bearing is over 360, with
full wrap-around.

One other things I just learned from this thread;
degrees:minutes:seconds is a supported format. Cute. Useful for optical
theodolites which are actually accurate enough to measure in such tiny
increments. Never seen it in a cave survey before.