A refractometer is a simple instrument used for measuring concentrations of aqueous solutions. It requires only a few drops of liquid, and is used throughout the food, agricultural, chemical, and manufacturing industries. A lensmeter or lensometer, also known as a focimeter or vertometer, is an ophthalmic instrument. It is mainly used by optometrists and opticians to verify the correct prescription in a pair of eyeglasses, to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames. Lensmeters can also verify the power of contact lenses, if a special lens support is used. The Chart Projector is an AC-powered device intended to project an image on a screen for vision testing. Ophthalmic examination chart projector including a rotatable chart carrying disc and a mask plate which are co-axial with each other. A phoropter is an instrument used to test individual lenses on each eye during an exam. Phoropters look imposing – like space-age visors – but are really an ingenious way to quickly determine the exact vision correction needed by your individual eyes. An optometry unit is a place where optometry is a specialized examination of the eye and related structures for defects or abnormalities. A lens edger matches the dimensions and shape of the optical lens with that of the frame to fit perfectly. Every optical lens's contour and thickness are unique depending on the form of correction a patient needs. Lens edging machines perform different functions, such as: basic automatic cuts.