The gauge is based on two flat steel plates, mounted parallel to each other. Embedded in the upper probe head are 33 capacitive sensors. A manually operated kind of drawer moves the wafer into the air gap between the two plates. The drawer is then lowered, the wafer comes to rest on the lower plate whose vacuum chuck is activated prior to the measurement. With every sensor in the upper probe plate, one measurement is performed. The measuring range covers the entire distance between the two plates at the given sensor position. The dielectric of the inserted wafer at a given point affects the measured result and is proportional to its thickness there.

• Material > 10⁷ Ohm*cm
  e.g. GaAs, Quartz
• Measures the dielectric not the distance
• Thk = Thk_m *  epsilon / (epsilon-1)
• Thickness
• No Bow or Warp
• Special material must be chucked to avoid the piezoelectric effect.