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Algebraic difference between a size and a corresponding basic size is called deviation. Limit deviations are upper and lower deviations. Algebraic difference of actual size with basic size is called actual deviation.

**Upper Deviation:** It is the algebraic difference between the maximum size and the basic size.

The upper deviation of a hole is represented by a symbol ES (Ecart Superior) and of a shaft, it is represented by es.

**Lower Deviation:** It is the algebraic difference between the minimum size and the basic size.
The lower deviation of a hole is represented by a symbol EI (Ecart Inferior) and of a shaft, it is represented by ei.