D0

Loads/returns the reference cube zero distance.

Mnemonic:

Distance 0(zero)

Syntax:

D0 [value]

value: The exact distance between the mirror center and the reference cube, in mm.

Return values:

Success:

D0 1, value

Failure:

D0 0, err_msg

value: The new or current D0 distance value.

err_msg: Should the command fail, this value will be an error message string, explaining the cause of failure. D0 may fail if:

• The parameter value is non-numeric.

Remarks:

D0 loads the precise distance from the mirror center to the reference cube. The reference cube phase is due partly to this distance, partly to the optical path between the mirror center and the rest of the instrument, and is also affected by electronic drift in the instrument. In order to eliminate the last two effects from the distance measurement, the reference cube phase is subtracted from the phase of the cube whose distance is being measured. However, this also subtracts the distance D0, which is not common to all other measurements. For the measurement to be accurate, this distance D0 must be added back to the cube's measured distance.

Example:

     send: D0 180.45
  receive: D0 1, 180.45

     send: D0
  receive: D0 1, 180.454

See also:

ALPHA, BETA, BP, COO, EZ, INITZY, MO