We have several dozen pressure transducers deployed in wells or in streams to measure water level, and sometimes it’s helpful to read the water level directly from the sensor. This model of sensor has an analog output, meaning that the circuitry supplies 5 volts DC to one wire, and the voltage on the return signal wire is proportional to the depth of the water. So by measuring the analog return voltage very precisely, we can get millimeter accuracy measurement. This particular display is mounted in a small enclosure about the size of a TV remote. It uses a very small LCD display and an ArduinoPro Mini. The board supplies a constant 5v to the sensor and then measures the sensor signal voltage using one of its analog input pins. At first, you have to collect a bunch of data showing the relationship between water depth and voltage by doing calibration tests at various precisely-measured water depths. Once you know that equation, you then reprogram the Arduino to take the analog reading and then apply it to the equation to calculate water depth, and then the Arduino displays that depth information on the LCD.