Apparatus and methods for measuring shape of both sides of a plate

An apparatus for measuring shapes of both sides of a plate, comprising:

• a surface plate disposed in such a manner that a reference plane of the surface plate is set in an almost vertical state;
• a holding mechanism which holds a plate to be measured in such a manner that a plate surface of the plate to be measured is set in almost parallel with the reference plane;
• a first displacement gauge and a second displacement gauge which are disposed between the reference plane of the surface plate and one surface of the plate to be measured which is held by the holding mechanism, the first and second displacement gauges being scanned in a vertical plane, and serving to measure a distance from the reference plane of the surface plate and a distance from one surface of the plate to be measured together with the scan, respectively;
• a third displacement gauge which is disposed on the opposite surface side of the plate, the third displacement gauge being scanned in avertical plane and serving to measure a distance from the opposite surface of the plate surface together with the scan;
• and
• calculating means for calculating a shape of a surface of the plate to be measured based on a measurement result by each of the displacement gauges.