When a contractor finds that something won't fit, or when the architect or owner thinks that the walls aren't vertical or straight or that the floors aren't flat or level enough, someone is unhappy with the degree of tolerance achieved. Maybe the construction operations weren't precise enough. Maybe the specifications weren't tight enough or clear enough. Maybe the structure as designed couldn't actually be built to the requirements specified. In any case, some accommodation must be made- by repair, adjustment or just plain acceptance of a bad situation. And, someone most likely will be disappointed. Part of our present situation in construction is that we are not entirely sure what degree of precision is needed in each individual circumstance, or what degree of precision can be achieved at reasonable cost. There is a need for all members of the construction industry to compare notes on what we want, what we really need, what practical considerations affect any particular degree of precision in building, and the relation of all this to cost. The immediate reason for specifying tolerances is to establish the ease of construction without the necessity of later modifying parts to fit together. A more long-range reason is to ensure that the structure will perform as needed, particularly with respect to safety. The parts of the structure should have adequate strength and be of such shape and dimensions that there is no danger of structural failure through movement of the parts. Joints should be sufficiently close to the design to perform properly and, where necessary, be capable of being sealed against intrusion of water, wind, dirt, and debris. Tolerances on the location of reinforcing steel should be adequate to ensure the placability of concrete all around the reinforcing cage. One recent advancement in the control of dimensions, elevations, plumbness, planeness, and alignment has been the introduction of lasers. Other methods of controlling tolerances are illustrated in the figures found in the article. Figure 1 shows three simple methods of checking deviations of angles. A template like that shown in Figure 2 can be used to measure warping. Warping of a vertical surface can be measured with a stadia rod equipped with leveling bubbles and dial gages. The rod is set in Position 1 near one vertical edge with the leveling bubble in a fixed position and the dial gages are adjusted to give a reading of the distance between the rod and the surface. The rod is then moved to Position 2 and held with the leveling bubble in an identical position. The distance that one dial gage has to be move in or out indicates the amount of warping.