When double clutching and shifting, which can tell you when to shift?

Answer: A — Tachometer

The tachometer is the instrument that tells you when to shift because it shows the engine’s speed in revolutions per minute. When you’re double clutching, you’re aiming to match the engine speed to the gear you’re selecting, so you time each shift by watching the RPM. Shifting as the engine reaches the proper RPM range keeps the engine from lugging (shifting too early) or over-revving (shifting too late) and makes the double-clutch process smoother. The other gauges don’t indicate engine speed: the speedometer shows road speed, the oil pressure gauge shows lubrication status, and the fuel gauge shows fuel level.