Why the long warm up time ?
Electronic components are subjected to heat during operation. They generally do not operate optimally until the temperature stabilizes. In theory digital electronic designs are immune to this, but there are no devices that are 100% digital...there are always analog circuits involved even if it's just the power supply, and it takes a little time for a power supply to fully stabilize its output voltages which can be critical. Many designs incorporate features to compensate for temperature change but none are absolutely perfect.
I often calibrate complex devices and voltages are sometimes read to five decimal places. That depends on the level of precision required.
