This instrument shows results and test options on a large, clear analog/digital scale for both practicality and precision. A built-in timer makes both spot tests and PI testing easier to carry out. They are powered by a built-in rechargeable lead-acid battery which can be charged directly from any supply from 95 V to 265 V. All testers incorporate a guard terminal to allow surface leakage to be removed. Pre-set standard test voltages at 500 V, 1000 V, 2500 V, and 5000 V are on the BM21 units with a variable test voltage in 25 V steps. These top-of-the-range units also allow measurement of resistance to 5 T?, leakage current to 0,01 nA, and can display capacitance at the end of a test to 10 F.