A hip resurfacing CAS system for guiding an operator in altering a femoral head in computer-assisted surgery for subsequent implanting of a femoral head implant, comprises a trackable reference on the femur. The high pressure rail is connected to the pump with a supply line. The second optical waveguide region is optically coupled to the first optical waveguide region and has a heater for changing a refractive index of the second optical waveguide region. 00, the esters formed have excellent solubility for paraffinic and naphthenic mineral oils and are therefore especially well suited for lubricating vehicle air conditioners formerly containing chlorine containing heat transfer fluids and mineral oil lubricants.