The number of digits you have in an instrument and the instrument's uncertainty play significant roles in your measurement. Use your measurements in calculations, and you can have more digits than make sense. You have to apply rounding techniques and use the proper notation to get meaningful numbers from your test equipment. A number's rightmost digit indicates its precision. Errors in readings Just because an instrument can display a small change in a signal doesn't mean the displayed value reflects reality.
All measurements carry an uncertainty.
Some of that uncertainty comes simply from the uncertainty in the rightmost digit's resolution while the rest comes from errors introduced by the measuring equipment's circuits. Manufacturers use different methods for expressing uncertainty, usually called accuracy in data sheets. These methods include a percentage of full scale, a percentage of full scale plus a percentage of reading, and a percentage of full scale plus a fixed number of display counts. Assume the following specifications. If you connect the meter to a 10.0000-V calibration standard, then any meter reading between 9.993 V and 10.007 V falls within the uncertainty specs of the meter.