Product Description An accurate way to measure the freezing point of radiator coolant or antifreeze, battery electrolyte It is fast and easy to use. Very clean. Just needs a drop of fluid on the prism and close the cover. The view-finder is adjustable so you can focus it to your vision. The large prism allows for maximum light to enter the unit for easy viewing. The indication is shown by the position of the light and dark border against the scale indicator.