The build-in automatic temperature compensation feature makes it get consistently accurate reading, no need to control the liquids temperature deliberately, just make sure it's at room temperature ( during 0-25 degree centigrade) . Just need to take of your liquids on the prisms and hold the refractometer to the light, then look through the eyepiece, you can get the reading. Features - Color: As shown. - Size: 19.50X4.00X4.00cm/7.66X1.57X1.57 inch. - Material: Metal, rubber. - Measuring range: 0-100%. -Note: cloth is color - The refractometer are based on the principle that the refractive indices of liquids change when the concentration change. - It's portable, easy, quick and no battery required, easier and more accurate than a traditional hydrometers, more than a digital meter. - It's a perfect for or young, home or professional use - The internal optical lens with high refractive index make up the precision optical system - It has a simple design, but very practical in use, giving you a Package list: 1 x Refractometer 1 cloth 1 x straw 1 x English manual 1 x screwdriver 1 x packing box