PURPOSE. The Type 1644-A Megohm Bridge (Figure 1-1) measures resistance from 10* to 10l* ohms. It is useful for measurements of resistors, of insulation resistance on components and machinery, for resistivity tests on samples of insulating material, and for leakage-resistance measurements on capacitors. The vernier (AR%) dial permits accurate measurements of voltage and temperature coefficient of resistance. The voltage applied to the unknown may be set from 10 volts to 1000 volts.