A telescopic multi-unit spirit level has a central housing in which the principal levelling unit is accommodated. A number of additional auxiliary levels located both in front of and behind the principal unit on telescopic arms are able to be fanned out from the housing in the manner of the blades of a pocket knife and aligned in any desired direction via articulated joints so that simultaneous observations can be made during a programme of measurement. When not in use the auxiliaries are clipped back into their storage positions in the housing.
