Automotive Instruments — What Does a Tachometer Measure? In standard passenger cars, the tachometer displays which operating parameter?

Introduction / Context:
The instrument cluster provides the driver with essential information. While the speedometer shows road speed, the tachometer serves a different purpose that helps with shifting, diagnosing engine behavior, and avoiding over-revving.

Given Data / Assumptions:

• Conventional dashboard with speedometer, tachometer, and other gauges.
• Engine is spark- or compression-ignition with a rotating crankshaft.

Concept / Approach:
A tachometer measures rotational speed, typically the crankshaft’s revolutions per minute (r.p.m.). It informs the driver about engine load relative to speed and gearing. On manual transmissions, it guides shift points; on automatics, it aids diagnostics. Modern electronic tachometers read signals from ignition systems or crank sensors.

Step-by-Step Solution:
Identify variable displayed: rotational speed of engine crankshaft.Unit: revolutions per minute.Match to option: “engine r.p.m.”

Verification / Alternative check:
Owner’s manuals and instrument legends label tachometers with ×1000 r/min scales.

Why Other Options Are Wrong:
Speed: shown by speedometer (km/h or mph).Distance: shown by odometer/trip meter.Fuel consumption: requires separate computer/gauge.Oil pressure: separate gauge or warning lamp.

Common Pitfalls:
Misinterpreting tachometer redline; sustained operation above redline risks engine damage.

Final Answer:
engine r.p.m.