What is Measurement?
Measurement assigns a number to a physical quantity using a standard unit. Engineers rely on precise measurements to build structures, design circuits, and test prototypes. Without accurate data, bridges can collapse, medicines can be mis-dosed, and machines can break down.
Precision vs. Accuracy
Accuracy describes how close a measurement is to the true or accepted value. Precision describes how consistent repeated measurements are — even if they are all wrong in the same direction.
Example: a scale that always reads 0.5 kg too heavy is precise (consistent) but not accurate. A scale that gives different readings each time but averages to the right value is accurate on average but not precise.
The SI System
Scientists and engineers use the International System of Units (SI). The seven base units include: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). All other units — such as Newtons or Joules — are derived from these seven.
Significant Figures
Significant figures (sig figs) indicate the precision of a measurement. For example, 12.30 cm has 4 significant figures — the trailing zero is meaningful. When multiplying or dividing measured values, the result should have the same number of sig figs as the least precise measurement used.
Measurement Error
Random error is unpredictable variation that causes measurements to scatter around the true value. It can be reduced by taking multiple measurements and averaging. Systematic error is a consistent bias (like a miscalibrated instrument) that shifts all measurements the same way — averaging many measurements does NOT eliminate systematic error.