The optical system is equipped with the incident angle of 45°and receiving angle of 45°for the portable reflectance instrument, of which both the alternating/direct current are used for the power supply. The sensor unit can be operated by one hand with handle switch type that makes on-the- spot measurement easier. The instrument can measure not only the flat mirror but the curved mirror with a radius more than 100mm,
almost in no errors. Apart from the front coated mirror, the thick rear coated mirror can be measured by changing an adaptor for the measurement window.