The resolution of a measuring instrument is the smallest division of the value it measures that can be detected by it. In Figure 1 the first ruler scale, in millimetres, has a better resolution than the second, in centimetres. It is possible to be confident in measuring to the nearest mm (3.3 cm) with the first scale. However, with the second scale, judging by eye introduces more uncertainty (a random error), perhaps measuring between 3.2 cm and 3.3 cm. The first scale is certainly better for measuring small distances, but for large distances, other unavoidable errors may be (much) bigger than its resolution.
For digital measuring instruments, resolution is no greater than the value of the smallest significant figure shown on the display. In Figure 2 two digital mass balances, with different resolutions, measure the mass of the same ‘100 g mass’, which has an actual mass of 99.624 g. The first records a value to the nearest gram, 100 (±0.5) g, and the second to the nearest 0.01 g, 99.62 (±0.005) g. The latter reading is more accurate, because it is closer to the true value of the mass. Using a scale with a greater (better) resolution can allow us to measure to a greater accuracy.
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