[Therion] sd for a vertical pole

[Tarquin Wilton-Jones]

Hi folks,

I guess this could just as easily be a Survex question as a Therion
question.

I have GPS readings taken on a pole, with the position being given for
the top of the pole. Subsequent Disto readings are taken from the bottom
of the pole. The pole is brought to vertical using a spirit level. I
have checked the accuracy of the spirit as being 0.125°.

I have the (measured) standard deviations of the GPS positions, so I can
specify the standard deviations for the location fix. What I need to
work out is how to specify the standard deviation for the pole. It's not
a plumb measurement, because it is not purely gravitational. So although
I could use "DOWN" that is not actually accurate, since it is really a
nearly-vertical measurement depending on the accuracy of the spirit
level. It's really a length and clinometer reading.

#length of the pole accuracy measurements
sd length 0.001 metres
#accuracy of the spirit level
sd clino 0.125 degrees

But when working with a supposedly vertical position, even the slightest
error in the clinometer angle of the pole could cause the compass
bearing to flip to any angle at all. But this seems extreme:
sd compass 360 degrees

So what would be the right way to specify it?

Cheers,

Tarquin