During the 19's, Schrödinger state that it is impossible to make a measurement without disturbing a system. To illustrate his statement, he made the famous experiment of the cat and the box. Poor cat btw..
This is also true in electronic nowadays. A multimeter is use in parallel of a load for a voltage measurement. This "add on" will change the equivalent resistor value and then change the "true" voltage value. This is also true for current or other kind of measurement.
How is it possible to compensate this lack of precision? I don't need to be that accurate, but I ask that question by pure curiosity