How to calculate the accuracy error?

The accuracy is typically denoted in the percentage form of the reading, that is 1% of the reading, for example, if the measured value is 100V, the actual value may be between 99V~101V. But for technical parameters, the least significant digit will be counted into the accuracy, for example, if the accuracy is ±(1%+2) and the measured voltage is 100V, the actual value will lie between 99.8 and 101.2V.