Accuracy vs. Precision. Calculations Involving Measured Quantities The accuracy of a measured quantity is based on the measurement tool. The last digit.

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Presentation transcript:

Accuracy vs. Precision

Calculations Involving Measured Quantities The accuracy of a measured quantity is based on the measurement tool. The last digit always represents a guess. Rule: When making measurements, estimate your measure to the closest tenth of the smallest scale.

Consider a line of length 5.85 cm using the ruler below: The final digit of 5.85 cm is an estimate of the nearest tenth of the scale. Using our rounding rule >> 5.85 cm = 5.8 cm Therefore our answer is accurate to 2 sig figs where “.8” is the least reliable digit.

Accuracy vs. Precision Accuracy: The number of significant digits within a measured quantity. Precision: The number of decimal places in a measured quantity.

Eg.1: For each value below determine a) The number of significant figures b) The accuracy of the value c) The precision of the value ValueI = cmy = 240 mz = x m a) b) c) I accurate to 5 sig figs 5 I precise to cm y accurate to 2 sig figs 2 y precise to 10 m z accurate to 4 sig figs 4 z precise to m