The P-21 optometer is designed for mobile use. It provides a wide dynamic range for the detectors’ signal currents ranging up to 2 mA. The noise-equivalent current signal is < 0.1 pA. Eight gain ranges that can be manually or automatically selected to match the signal levels. It offers a large color touchscreen and three manual buttons for versatile usage. The intuitive menu and analog interfaces make this device an all-in-one solution.