Absolute reflectance measurements directly measure the reflectance of the sample without the need for a reference sample. However to verify that the accessory is properly aligned and the system is providing accurate data,, periodic checking with calibrated mirror is recommended. Absolute reflectance measurements require an accessory in which the optical path is identical except for the presence or absence of the sample. The V-N optical configuration is a convenient way of achieving this. The V-N accessories are used in combination with an integrating sphere detector, and depolarization is required for angles greater than 15 degrees. Typical applications include front and back-surface reflectance, and anti-reflection coatings.