# Wavelength adjustment for a Velocity Selector

The wavelength selected by a neutron velocity selector depends on the tilt angle of the selector and its rotation speed. This is what the velocity selector wavelength command is for. It is usually installed into the system as lambda. This variable can be driven using the normal drive and run commands. Additionally this command understands a few sub commands. For the following discussion is assumed that the name of the command is lambda.

lambda
  The name of the variable alone prints the current wavelength in nm.
lambda rot val
  calculates the rotation speed for the wavelength given by val.
lambda wl val
  calculates the wavlength for the rotation speed given as parameter val.