[Therion] Detecting errors

[Tarquin Wilton-Jones]

This is one of the reasons that for legs like that (where the Disto will be parallel to a wall not perpendicular to it during the next shot), we aim the laser not for the station itself, but for the middle of a small block that is a similar size to the Disto, held on the station. The easiest thing to use is the nail varnish bottle which will be used to physically paint semi-permanent stations. It is easier to see from a distance, and it removes angular and distance errors you mention. And the person holding the nail varnish can clearly identify whether the Disto missed the target.For calibration, I get a typical error of around 0.3 or below. All metal objects are removed first: tripods, tackle bags, krabs, belt, Android device, stylus, helmet, light, SRT gear, wedding ring, watch, safety knife, etc.. And avoid fixed aids like bolts or cables, or areas with scaffolding or fences and gates, or reinforced concrete in the cave.I use obvious natural marks on the walls for all points of the calibration, aiming from one to the opposite one, about 3 metres (10 feet ish) apart. Then the opposing measurement in the opposite direction. This is done for all measurements, horizontal, vertical and diagonal.When the cave has natural minerals, avoid those areas during calibration. For our lead mine surveys, we calibrate in a local forest where there are no minerals.
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