Tangent Plane

Applies a surface control to a simulated tangent plane made from the high points of a surface.

REFT

The tangent plane modifier evaluates the theoretical tangent plane contacted by the high points of an irregular surface.

The surface elements themselves are not all controlled by the zone; only the simulated tangent plane must satisfy the orientation requirement.

Use it with related surface controls such as parallelism, perpendicularity, or angularity.

Add a separate form control when flatness of the actual surface elements is also important.

Tangent Plane Drawing Use

Tangent Plane is read with the adjacent dimension, note, or feature control frame so inspection uses the intended feature definition.

DATUM

This modifier changes how a related dimension, note, or feature control frame is interpreted.

Read the symbol with the attached dimension, note, or feature control frame before evaluating the feature.

Verify the controlled feature using the drawing's stated limits, datum setup, and any special notes tied to the symbol.

A drawing includes the Tangent Plane symbol with a related feature requirement.

Identify

Recognize the Tangent Plane symbol and the feature it modifies.

Read

Adjacent value

Use the attached dimension, note, or frame cells as the controlling requirement.

Inspect

Per drawing

Measure the named feature using the specified interpretation rather than assuming a generic size check.

Tangent Plane clarifies how the feature is defined so the drawing and inspection method stay aligned.

Item	Controls	Typical Placement
Tangent Plane	Requirement interpretation	Next to a dimension, note, or frame
GD&T control	Geometric variation	Feature control frame
Datum reference	Measurement setup	Datum feature or frame cell

This page is part of the drawing-symbol reference set rather than a standalone geometric tolerance category.

When the symbol modifies a feature control frame, read it together with the tolerance value and datum references.