If a meter with the indicated specifications is set for the 0-to-80-volt range, small values would be accurate to within 10mv, while larger values could be off by an additional 24mv. On such a meter, the last digit will generally not be meaningful when taking a single reader in isolation, but is provided for use in situations where one is interested in the differences among readings that are taken very close together. For example, if measures two voltages in fairly quick succession, and then repeats those measurements, and the readings are:
49.123V 49.569V -- Initial measurements
49.125V 49.568V -- Repeated measurements
one then the difference between the two items' voltages could be safely said to be somewhere between 442 and 445 mV. One wouldn't know where the first voltage was within the range 49.10V and 49.15V, nor where the second was within the range 49.55V and 49.59V, but one would know the difference with a precision much greater precision than one knew either voltage individually.