Sometimes near enough just isn't good enough - we have to have precision. Eurorack modular synthesisers use the Volts per Octave standard for pitch control, where a change of exactly one Volt in pitch CV results in an exact one octave change in pitch from the oscillators. Even small inacurracies in voltage can lead to quite large changes in pitch, so for transposition and control voltage addition it is important to have a very accurate voltage source and adder to keep everything in tune.
The Precision Voltages can be used as a super accurate voltage source, voltage adder or both at the same time. It has two channels to which voltages representing Octaves and Notes can be added or subtracted. If there is no input to a channel then it behaves as is a voltage source, or if an input is added to that channel then it becomes a very accurate voltage summer that can add a precise voltage to the incoming voltage.
Channel A also allows an external Gate signal to be used to turn on and off voltage addition while still passing the input signal to the output unchanged. We also have a useful Combination Mode, where channel B can be added or subtracted from Channel A.
A calibration output is also included which has an accuracy of +/-0.5mV so that it can be used instead of expensive test equipment to calibrate VCO's and similar modules.
More information you can find here: Precision Voltages