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Straightness Tolerance Straightness is the property possessed by the curving of a line or surface. There are 2 kinds of straightness:
• Straightness of an axis or centre plane
• Surface straightness which is determined by the placement of the feature control frame
The geometric characteristic symbol for straightness is a horizontal line. Straightness is a condition in which each line element of a surface, or an axis, is a straight line.

Straightness tolerance controls:
• Straightness of a line on a surface
• Straightness of a line in a single plane
• Straightness of a line that is the axis of a feature
• Centre plan control
A straightness tolerance specifies a tolerance zone within which the considered element or derived median line must lie. A straightness tolerance is applied to the view where the elements to be controlled are represented by a straight line. The tolerance value is the specified distance between two parallel straight lines, two parallel planes or the diameter of the tolerance zone cylinder.

If the symbol φ is attached before the numerical value that indicates the tolerance range, this tolerance range is the range within a cylinder of diameter t.

If a tolerance frame is connected to a dimension that indicates the diameter of a cylinder, the axis line of the cylinder shall be contained within a cylinder of 0.08mm diameter.

Two common uses of the straightness form control are:
1. Straightness as a surface element control
2. Straightness as an axis or centre-plane control

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