There are fourteen types of geometric tolerances, often grouped into these five categories: Form, Orientation, Location, Profile, and Runout.
The tolerance topics below go through each tolerance type. Those topics provide details about what each type means, its allowed modifiers, and allowed command options.
Form tolerances are the simplest because they do not reference datums:
You can find further details in these topics:
Actual and Measured Values
For each geometric tolerance type, we distinguish between “actual values” and “measured values.”
An actual value deals with the specification, and it is defined by a specification standard like ASME Y14.5.1 or ISO 1101. An actual value uses all the points of the surface, with no measurement uncertainty. This value tells us whether the surface conforms to its specification or not. It gives us some idea how close a conforming surface is to non-conformance.
A measured value is a measured approximation to an actual value. The measured value uses some subset of the points of the surface. Each measured point of the surface includes measurement uncertainty. The algorithms we use to derive a measured value may or may not be similar to the mathematical definition of the actual value. This is because sometimes the best measured approximation to the actual value uses very different mathematics than the actual value uses.
For more information, refer to "Specification Versus Verification".