I'm researching a WWII airfield near where I live in Devon, U.K.

It appears that the meteorologists used balloons as part of the data
collection, but at that time they had no radar, etc., to help with finding
the height of the balloon.

The control tower of this airfield was equipped with two pillars to which
theodolites could be attached/mounted. Apparently, these were used to
determine the angle of ascent and the height of the balloon.

Does anyone have any idea how that could be done, given (as far as I can
see) that you need the horizontal distance to the balloon as well as the
angle to find the height? Or would the use of two theodolites
simultaneously, spaced at about 22 feet apart, allow the height to be
found without needing the horizontal distance?

TIA.

Brian Salt.
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