The Advantest R6581T is an 8.5‑digit, rack‑mount digital voltmeter (DVM) built for high‑precision DC measurements; the T variant is a DC‑only field/rack model (no AC TrueRMS option) and is prized on the used market for lab and calibration work—buyers should expect to source units secondhand and verify display/health before purchase. Overview Notable Features and Design…