Single VOAC7523/7520 unit, equipped with a 2-channel DC measuring input and dual display, can perform DC voltage measuring that normally requires two units and thus saves installation space and improves measurement speed. The VOAC7522/7521A, equipped with one input channel and dual display, can perform current or frequency measuring simultaneously with voltage measuring. The VOAC7522/7523 realizes the high resolution of direct-current voltage measuring at 0.1μV and broad bandwidth of alternating voltage at up to 300kHz.