A phase-shift motor step size (full or half).

Input Format:

One of the following:

• full - Position the phase-shift motor to within a full step of the requested position.
• half - Position the phase-shift motor to within a half step of the requested position.

Context:

The phase-shift motors in the receiver cryostats are stepper motors. The resolution of these motors is thus nominally one step, but, at the expense of having to keep the motor coils continually energised, one can alternatively hold the motor half way between two steps, thus doubling the accuracy with which the motors can be positioned. The PhaseStep datatype is used with the pshifter command to specify which of these two modes to use.