Measurement and Applied Science
Domain focus
Measurement and Applied Science tests SI units, precision instruments, tolerances, clearances, pressure, force, and thermal effects. Accurate measurement underpins every diagnostic and repair decision.
Core rules
- SI units: metre, kilogram, second, newton, pascal, kelvin, ampere, volt, ohm.
- Vernier calipers typically read to 0.02 mm; micrometers to 0.01 mm; dial gauges to 0.01 mm or finer.
- Zero error must be checked and applied before measuring.
- Tolerance is the permitted deviation from nominal size; clearance is the gap between mating parts.
- Thermal expansion can change clearance: ΔL = α × L × ΔT.
- Torque wrenches require calibration and correct use at the specified range.
Worked example
A micrometer shows 7.5 mm on the barrel and 28 divisions on the thimble. With a 0.01 mm thimble, reading = 7.5 + 28 × 0.01 = 7.78 mm. If the zero reading is +0.02 mm, the corrected value is 7.78 − 0.02 = 7.76 mm. The reasoning shows why zero error and thimble division value must be confirmed before accepting a measurement.
Traps
Ignoring zero error, reading a vernier from the wrong scale line, and mixing millimetres with centimetres. Parallax and temperature also affect readings. A torque wrench used below its calibrated range may be inaccurate even if it clicks.