Surface plate: it is the plane datum instrument with steady performance and reliable precision which is used to inspect and line.

Platform: surface plate is also called platform.

Working surface: it is the datum plane of workpieces’ inspection or lineation.

The main supporting point: it is used for main supporting parts when processing, verifying, using and installing datum plane or contacting with special stand. The supporting force here is static state.
Auxiliary supporting point: when using the surface plates in case of any harmful deformation cause by centre-of-gravity shift or heavy-load, auxiliary supporting point is added.

Supporting force on the auxiliary supporting point should be lower than which is on the main supporting point.