24 Geometric Dimensioning and Tolerancing Copyright Goodheart-Willcox Co., Inc. Geometric tolerancing uses basic dimensions and positional tolerancing with cylindrical tolerance zones to overcome tolerance buildup. As previously discussed, a basic dimension is a dimension that is considered theoretically perfect in size, profile, orientation, or location. Basic dimensions are the basis for variations that are estab- lished by other tolerances. Example 1-21 shows the tolerance zones of the holes posi- tioned at their theoretically exact locations. N O T E ASME Y14.5-2018 eliminates plus and minus tolerancing and limit dimen- sioning for location dimensions. These methods are documented as alter- native practices when applied to surfaces. Location dimensions that apply to regular features of size are basic from datum features with positional tolerances. Location dimensions between surfaces are basic from datum features with profile tolerances. Only size dimensions have plus and minus tolerances or limits defined by limit dimensions. Orthographic View Tolerance Buildup 15.25 40.25 0.5 Tolerance 1 Tolerance 14.75 39.75 Rectangular tolerance zone Goodheart-Willcox Publisher Example 1-20. Tolerance buildup occurs when using chain dimensioning with coordinate tolerancing.