Bull's eye level

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A Bull's eye level is a type of spirit level that allows for the leveling of planes in two dimensions - both the 'pitch' and 'roll' in nautical terms. Standard tubular levels only consider one dimension. Bull's eye levels are used primarily by carpenters in construction, but can also be found as features of compasses or other devices that need to be kept from tipping in certain directions (whether it be for functionality or precision of measurements). Another name for a Bull's eye level is a "circular bubble" which is the name used by surveyors in the United Kingdom. Surveying instruments such as theodolites (transits) and total stations often have a circular bubble as well as a tubular level or "plate level". The circular bubble is used to roughly level the instrument in two dimensions and then the plate level, being more precise, is used to level the instrument more precisely in each dimension separately by levelling the plate level, the spinning the instrument 90 degrees and levelling the plate level again.