Mercury - Tachometer 6K Engine Speed Monitoring Black Face Chrome Bezel 79-8M6020001. OverviewThis 6,000-RPM tachometer gives you a steady, no-drama read on engine speed while you're running. The needle moves in a slow, calm sweep, so you're not chasing jittery numbers every time the hull shifts. On the water, it feels natural to check-quick look, quick answer, back to the throttle. It's a clean, simple gauge that fits right into everyday boating without drawing attention to itself.. Key Feature