Asource of variation that is inherent in a system and predictable is typically known as:

The right answer is common error.

A common error (or random error) is when, from one measure to another, the value obtained may be overvalued or underestimated in relation to the real value.

An example of a random error is the measurement of time with a timer. The error comes from the reaction time of the experimenter at start-up and at the end of the timer. Since this reaction time is not always the same, the measured value can be overestimated or underestimated. It is understandable that a repetition of the measures can alleviate the random error.

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this protocol provides a detailed procedure for nucleoprotein extraction from cultured cells and tissues in an efficient manner.