To set up the observing posts a baseline had to be established and the posts co-ordinates established by an open traverse and triangulation from known points. This was a matter of pure survey work. It involved measurement of angles and distances. For the former we were trained to use the very best Wild Swiss made theodolites (each secure in a stout steel case) with its tripod which again had to be level and centered over a precise spot, and in measurement over distances by surveyors chain, using arrows (to count the number of chains) and banderoles (surveyors poles to keep a straight line).
We had to get precise results in our rounds of angles by taking at least three observations between the stations and getting them to agree. (I can recall even now three of the points we observed on training, the Bustard wind pump, out to the west on the Plain, Shrewton water tower and Knighton quad, up on the Down as I’m sure can many others who trained at Larkhill can also remember.)
This involved working as a team. When using the theodolite, one the observer, took the round of angles, (to degrees, minutes and seconds) the other booked them and if acceptable by their closing, a third relayed the information back to base over a land line laid by our signalers or by radio. When measuring, one booked and kept the line straight whilst the others laid the chain.
To get the hang of the drill in using the Simms, we spent many an hour as both observers and calculators on an indoor range in one of the huts so set up to represent a vista over an expanse of country. Here we observed mock gunfire simulated by flashing lights, identifying a flash and by bringing the other observers on to it, taking the bearings and passing them back to our HQ. And there using those cross bearings from known co-ordinates to calculate using trigonometry and at great speed with our logarithmic tables the position of the enemy gun. In the real world that was then sent back to our own guns for counter battery fire.
Once experienced we exercised out on the Plain making our traverses and taking our rounds of angles in setting set up a base, and observers posts and working from a field headquarters where the calculations were done. It was even more realistic when after setting it all up we participated in live shoots having a Battery of 25 pounder guns firing at the targets we had observed. This was great fun.
Very quick and accurate was this counter fire as the guns several miles to the rear could immediately be laid and fired from their co-ordinates on a specified range and bearing to the co-ordinates of the target. Our targets were old tanks out on the Plain and it was satisfying (and exciting) to observe the fall of the shells and explosions and see just how good our survey work and observation had been.