A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit.
Demonstration analog voltmeter
Two digital voltmeters. Note the 40 microvolt difference between the two measurements, an offset of 34 parts per million.
Analog-to-digital converter
In electronics, an analog-to-digital converter is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities.
4-channel stereo multiplexed analog-to-digital converter WM8775SEDS made by Wolfson Microelectronics placed on an X-Fi Fatal1ty Pro sound card
AD570 8-bit successive-approximation analog-to-digital converter
INTERSIL ICL7107. 3.5 digit (i.e. conversion from analog to a numeric range of 0 to 1999 vs. 3 digit range of 0 to 999, typically used in meters, counters, etc.) single-chip A/D converter
ICL7107 silicon die
