Digital multimeter accuracy calculation
The accuracy of a multimeter is also referred to as uncertainty by some manufacturers, usually stating "within one year of leaving the factory, measured at an operating temperature of 18 ° C~28 ° C (64 ° F~82 ° F) and a relative humidity of less than 80 [%], ± (0.8 [%] reading+2 characters)." Many buyers or users are not very clear about this and often ask. I assume here that there is an instrument that, in a certain range, such as DC 200V, is written like this, and the measured value is displayed as 100.0 on the instrument. So, what should be the correct value at this time. I think for ordinary users, they can completely ignore accuracy calculations and simply assume that DC 100V is sufficient. According to the manufacturer's accuracy calculation, when measuring 100V (displaying 100.0), the error is ± (0.8 [%] * 1000+2)=± 10, which is an error of 1.0V. When substituting the reading, do not consider the decimal point, use the displayed value to calculate. The calculated value should add the decimal point and then use the original reading to calculate the shipping cost. For example, the correct value is 100.0 ± 1.0, which should be between 99.0 and 101.0V DC.
The difference between three and a half digit and four and a half digit digital multimeters
Three and a half digits are also called 31/2 digits (pronounced as three and a half digits), and four and a half digits are also called 41/2 digits (pronounced as four and a half digits). We know that the accuracy of an analog quantity, after quantization and conversion into a number, is related to the number of digits. The more digits there are, the closer it is to the original value and the more accurate it is (generally speaking, without considering other situations, if the quantized value is 1.00000V, representing it with one digit is the same as representing it with N digits). So in general, the more digits there are, the more accurate it is, that is, four and a half digits are more accurate than three and a half digits.
