The Smart Tweezers Offset Calibration Board is a dummy PCB with holes placed at variable width to represent many different component sizes (0201, 0402, etc.). When Smart Tweezers or Colibri is set to 10kHz and the tips are placed at the minimum distance in the respective holes to the size of component being measured, the device will show the actual offset capacitance. This value then should be subtracted from the component's measured value for higher accuracy measurements.
Previously, the offset value had to be determined by holding the tips of the device at roughly the same width as the components leads. This lead to inaccurate measurements.
When using the Smart Tweezers devices, the Offset Subtraction value can be set using the Smart Tweezers Offset Calibration Board.