The Model 81001-A Wattmeter, identical to the Model 81000-A, has the added feature of an A/B switchable DC input, providing the option of single meter measurement of several power sources. Line sections are permanently installed at these measurement points, with Model 81001-A connected to each as needed (10 foot cable is normally supplied). The DC signal is coupled from the line section to the switchable DC input to provide the same measuring capabilities as the basic Model 81000-A.Your confidence in the quality and dependability of the 81001-A Wattmeter is assured with the Coaxial Dynamics Two Year Limited Warranty. A/B Switchable DC Input Shock Mounted “Taut Band” Meter 4-1/2″ Mirrored Scale Quick Match Connectors Internal 7/8″ Line Section Uses Standard Gold Plated Plug-In Elements Two Year Limited Warranty