The 7000 Series volt maintenance system is said to bring precision dc voltage metrology within the reach of more commercial and institutional calibration laboratories. The heart of the system is a zener-diode-based, 10V reference module that can achieve a stability of better than 1 ppm/year. By configuring up to 10 reference modules into the system chassis, users can create statistical references in which the outputs are averaged to produce a drift rate predictable to ±0.15 ppm/year, a noise level of less than 0.015 ppm, and a temperature coefficient of less than 0.02 ppm/°C. The system chassis has an integral digital null detector that performs inter-comparisons between individual reference module outputs and the average output or between the average output and an external 10V reference source. Linked to a PC running the company's 7050 software, all measurements can be automated. Pricing for the system starts at $4,999 and the 10V reference module is $3,295.