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Appendix B: Care & checking of equipmentCare and maintenanceSite engineers are responsible for the day-to-day care and maintenance of instruments. All setting-out instrumentsshould be packed and stored in secure, dry conditions when not in use. After use, if wet, instruments should bewiped down and left to air-dry before packing away. Lenses should be regularly cleaned using lens tissue or adusting brush. Instruments (and tripods) are expensive and must not be left on site unattended, even for shortperiods. Damage or total destruction is often caused by mobile plant. When carrying instruments by road, ensurethey are secured in the vehicle. Avoid carrying instruments out of their boxes over long distances and avoid carryingthem still attached to the tripod as this places unnecessary strain on the bearings.Adjusting instrumentsWhen adjusting instruments, always follow the manufacturers’ instructions.Checking levelA level should be checked at least weekly (two-peg test): from X, take readings a and b apparent difference in level of A from B = a − b from Y, take readings c and d if [(a − b)−(c − d)] is more than say, 3 mm, the instrument requires adjustment.Checking theodolite or Total StationPlate bubble: Set up the instrument until the bubble tube is parallel with two foot screws, and level the bubble. Turninstrument through 90°, level bubble using third foot screw. Turn back through 90°, re-level bubble if necessary. Thenturn through 180°, the bubble should still be central if correctly adjusted. If necessary, adjust according tomanufacturer’s instructions.Optical plummet – two types:1 Fixed in tribrach:– level tribrach with instrument or plate level over point defined by a cross. With a sharp pencil, trace theoutline of the tribrach base plate on the tripod head. Carefully turn the tribrach through 120° keepingwithin the marks on the tripod. Re-level and sight the cross. Repeat, turning through a further 120°.The cross should be central each time.2 Revolving plummet fixed in instrument or plate level.– level and centre over a fixed cross and rotate through 120° and 240° observing the cross, which shouldstay central each time. Horizontal circle: set up and level the instrument. Sighting a well-defined distantpoint, read the horizontal angle scale (H1). Transit the telescope and re-sight the point on the oppositeface, read the horizontal angle scale (H2). The difference between H1 and H2 should be 180°.Vertical circle:– set up and level the instrument. Sighting a well-defined elevated point, read the vertical angle scale(V1). Transit the telescope and re-sight the point on the opposite face, read the vertical angle scale(V1). (V1) and (V2) should be equal.Trunnion axis:– set up and level the instrument. Sight a well-defined high-level point with the centre of the cross-hairs.Depress the telescope and read a tape set close to the instrument (T1). Repeat this on the oppositeface and read the tape again (T2). The readings (T1) and (T2) should be equal.Checking rotating laserCarry out ‘two-peg’ test as illustrated opposite and adjust according to the manufacturer’s instructions.CIRIA C709121