Acarpenters spirit level should not be used for setting out the level of anything more than incidental work. It is not sufficient, in conjunction with a straight edge for instance, for getting a floor screed uniformly level. It is difficult to get concrete floors uniformly level to an accuracy better than 5 mm, and a contractor should always be warned when greater accuracy than this must be obtained with concrete. Usually discrepancies of 5 mm can be taken up in the floor screed of granolithic or terrazzo ground down to the desired smooth finish. To get tiling accurately laid, small pieces of tile are mortared onto the floor base at intervals across it, their level being fixed precisely to the correct finished level by use of the instrument level. Astraight edge is then used to keep the finished tiling at the right level between tile pieces, which are cut off as the work proceeds.
There are, however, some experienced tradesmen who exhibit astonishing skill in tiling an area perfectly level given only one level point.