3-1/2 Digit Display:

The number of digit positions used in a digital meter determines the resolution. Hence a 3 digit display on a DVM for a 0 —1 V range will indicate values from 0 — 999 mV with a smallest increment of 1 mV. Normally, a fourth digit capable of indicating 0 or 1 (hence called a Half Digit) is placed to the left. This permits the digital meter to read values above 999 up to 1999, to give overlap between ranges for convenience, a process called over-ranging. This type of display is called a 31/2 digit display, shown in Fig. A

Fig. A                                            Fig. B

4-1/2 Digit Display:

In case of 4-1/2 digit display, there are 4 full digits and 1 half digit. The number obtained is from 0 to 19999. For this operation the time period required for counting operation should be reduced. This can be achieved by changing the frequency of the clock signal. The wave shaping and amplifier circuitry should be more accurate for 4-1/2 digit display. The resolution of 4-1/2 digit display is better than 3-1/2 digit display while the accuracy is 10 times better.