The US Balance Professional WO-USY-300 is equipped with automatic backlight system. Backlight will automatically turn on with weighing operation,and will turn off automatically about 5 seconds if the weight does not fluctuate. The professional scale will automatically turn off after 10 seconds if you discontinue use, to save battery consumption. During weighing operation, when weihgt is determined, a lock symbol will appear. This professional scale is ideal for jewelry stoers gun shops laboratorys and the medical field.