It is a fact of life that all items of identical design and material specifications are not mathematically equal. But how much tolerance form the desired level of accuracy can be permitted with concrete? The problem must be separately analyzed for the various components making up a concrete job: (1) preparation and holding the shape of the forms; (2) installing and holding the position of the reinforcements; (3) proper handling and curing of the concrete as it gains strength; and (4) aging and volume changes in the hardened concrete. There is no reason why the shape of concrete should differ so much from the dimensions planned by the designer. In one luxury cooperative apartment building the floors were found to be as much as 2 inches out of level. The fault came form unequal wedging of the posting to level up the forms and this wedging probably continued during the concreting. Lateral distortion of beam and wall forms is also common. In one public building project in New York, the contractor was required to chip and replace concrete so that a stone facing would meet the required tolerance. Expenditures for the is job ran into almost half a million dollars. There is no justification for any work exceeding the tolerances listed in ACI 347-63. Misplaced reinforcement is often uncovered when investigating a structural distress. Missing bars are also a common discovery. Collapsed chairs have been discovered and sometimes all the top steel has been discovered sitting directly on the bottom steel. Tolerances for positioning the steel are also listed in ACT 347-63. There is no reason why these tolerances cannot be reasonable performed. It is also most important to keep the bars in proper position until the concrete has hardened. The change in dimension and internal stress resulting form aging are seldom considered by the designer. Time-dependent shrinkage of precast members, locked into position by welded connections or bonded continuity has caused serious cracking. Differential shrinkage between combinations of lightweight and normal concrete has torn the junctions apart. All of these troubles can be eliminated by allowing for future dimensional change and by proper details to connect the components with freedom of longitudinal movements and rotational variation.