I'll skip most of the introduction – Wookey gave a good overview on this topic in CREG Journal 52. Our aim is to replace the mechanical sighting instruments (clino, compass) and tape measure with something more easy (and hopefully at least as accurate) to operate. We don't need to consider measuring distances – this task has been solved by various incarnations of the Leica Disto or other laser rangers, which are (not cheap but) readily available. In contrast, only few people need a precise compass. Surface surveying is done using theodolites, which are much more precise than any device relying on the earth magnetic field. Even fewer people need an electronic compass that can be tilted (not to mention those who need to know the tilt, too). Well, we do – but this market is very small and so is the number of available products. In this article, I'll focus on the electronic compass/clino combination, Wookey already discussed other (inertial or GPS-style) instruments. In particular, I'm going to assume that we're going to have an instrument with three magnetic field sensors, two axis tilt measurement and an attached laser pointer for aiming. I'll call the two inclination angles "tilt" (the one you'd like to measure) and "roll". (...)
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