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Objective: Differentiate between accuracy and precision.

 Exact number – a number that has been determined as a result of counting.  The main emphasis of mathematics.  Approximate numbers – inexact number resulting for the measurement process.  Usually how most technical data are collected  Better the measurement device, the better the measurement.

 The accuracy of a measurement refers to the number of significant digits.  Significant digits – the number of units we are reasonably sure of counting.  They include all the known digits recorded from an instrument plus one estimated digit.  The greater the number of significant digits, the greater the accuracy.

Determining Significant Digits 1. All non-zeros are significant 156.4 m has four significant digits (measurement indicates 1564 tenths of meters) 2. All zeros between significant digits 306.02 km has five significant digits (measurement indicates 30602 hundredths of kilometers) 3. In a number greater than 1, a zero that is specifically tagged, such as by a bar above it, is significant 230̄ 000 km has three significant digits (measurement indicates 230̄ thousands of kilometers)

4. All zeros to the right of a significant digit and a decimal point are significant. 86.10 cm has four significant digits (measurement indicates 8610̄ hundredths of centimeters) 5. In whole-number measurements, zeros at the right that are not tagged are not significant. 2500 m has two significant digits (25 hundreds of meters) 6. In measurements less than 1, zeros at the left are not significant. 0.00752 m has three significant digits (752 hundred- thousandths of a meter)

 Scientific notation  The first factor indicates the number of significant digits.

 Precision – refers to the smallest unit with which a measurement is made, that is, the position of the last sig. fig.  385 000 km has a precision of 1000 km  0.025 g has a precision of 0.001 g  0.0500 s has a precision of 0.0001 s  12.3 m has a precision of 0.1 m

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