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Burunduk said:Could the "DIA" text following the tolerance value instead of the diameter symbol before it also be attributed to the old age of the drawing?
Geometric Tolerances. Geometric tolerance, or "tolerance of form" specifies "how far actual surfaces are permitted to vary from the perfect geometry implied by drawings."* The term "geometric" refers to the various geometric forms, as a plane, a cylinder, a cone, a square, or a hexagon. Theoretically these are perfect forms, but since it is impossible to produce perfect forms, it may be necessary to specify the amount of variation permitted. Geometric tolerances define conditions of straightness, flatness, parallelism, squareness, angularity, symmetry, concentricity, and roundness.
*ASA Y14.5-1957.
Since it is very expensive to maintain accurate geometric tolerances in the shop, tolerances of form should not be specified except when established shop procedures cannot be depended upon to produce the necessary accuracy.