The operating handle is an integral component of
  the blade assembly which provides direct control
  of the blade, with an external indicator showing
  blade position.

  To operate the handle and blade assembly, first
  ensure that the thermal link cartridge is loose,
  then rotate the handle to the desired position.
  Tighten the thermal link cartridge until contact is
  made with the regulating cam ensuring the
  cartridge locates a slot, then finally tighten the
  locking nut to the case.