FIGURE 5.16 Digital multimeter block diagram. (Courtesy of Fluke Corp. Reproduced with permission.) the flexibility of allowing voltages to be measured over wider dynamic ranges with suffi- cient resolution, an input voltage divider is used to scale the input voltage. A block dia- gram of a complete DMM is shown in Fig. 5.16. To allow measurement of ac voltages, a rectifier is included in the meter design. Since the accuracies of rectifiers are not as high as the accuracy of the dc voltage measuring circuitry of the DVM, the overall accuracy of ac voltage measurements is lower than when measuring dc voltages (ac voltage accuracies range from t0.012 to t 1 percent t 1 digit). Currents are measured by having the DVM determine the volt- age drop across an accurately known resistance value. Although the value of a resistor can be very closely specified, there is some additional error owing to the resistance change as a function of the heating effect of the current passing through the resistor. In addition, caution must be exercised when using the current-measuring function. Care must be taken not to allow excessive current to be passed through the resistor. Typical accuracies for dc current measurements range from t0.03 to t2 percent of reading tl digit, while ac current accuracies are 10.05 to 12 percent t1 digit.