**OBJECTIVE:**To understand how uncertainty in a measurement arises. To learn to indicate a measurement’s uncertainty by using significant figures.

Every measurement has an uncertainty.

- This is due to the sensitivity of the instrument or the ability of the users.

Because the last number is based on a visual estimate, it may be different when another person makes the same measurement. For example, if five different people measured the pin, the results might be

**Person**

**Result of Measurement**

1 2.85 cm

2 2.84 cm

3 2.86 cm

4 2.85 cm

5 2.86 cm

Note that the first two digits (2 and 8) in each measurement are the same regardless of who made the measurement; these are called the

The reason why the last place of the measurement is different because the users made an estimation. This estimation represent the uncertainty.

When you record your measurement, you will always write down all certain number plus 1 uncertain number.

**certain numbers**of the measurement. However, the third digit is estimated and can vary; it is called an**uncertain number**.The reason why the last place of the measurement is different because the users made an estimation. This estimation represent the uncertainty.

When you record your measurement, you will always write down all certain number plus 1 uncertain number.

- The number recorded in a measurement are called
**significant figures**.