# What is the uncertainty of a ruler?

**Ruler**A has an

**uncertainty**of ±0.1 cm, and

**Ruler**B has an

**uncertainty**of ±0.05 cm. Thus, (a)

**Ruler**A can give the measurements 2.0 cm and 2.5 cm. (b)

**Ruler**B can give the measurements 3.35 cm and 3.50 cm. Figure 2.2 Metric

**Rulers**for Measuring Length On

**Ruler**A, each division is 1 cm.

A.

### What is the uncertainty of a micrometer?

Consider as an example the micrometer caliper shown in Figure 3. The screw of this instrument has 2 threads per millimeter so that it advances .5 mm for each revolution. Since there are 50 divisions around the rim, the least count and the uncertainty of this instrument is 1/50 x

**0.5 mm**=**0.01 mm**.#### What is the uncertainty of a meter?

Therefore the instrument uncertainty for the meter stick is**±0.1 cm.**(± smallest division). Sometimes, one can estimate the instrument uncertainty by interpolation. The interpolation is usually estimated as a multiple of ½, 1/3 or 1/5, etc of the smallest division on the instrument.#### What is the uncertainty of a thermometer?

According to British Standards, correctly calibrated, used and maintained liquid-in-glass thermometers can achieve a measurement uncertainty of**±0.01 °C**in the range 0 to 100 °C, and a larger uncertainty outside this range:**±0.05 °C**up to 200 or down to −40 °C,**±0.2 °C**up to 450 or down to −80 °C.#### What is a zero error?

AQA Science: Glossary -**Zero Errors**. Any indication that a measuring system gives a false reading when the true value of a measured quantity is**zero**, e.g. the needle on an ammeter failing to return to**zero**when no current flows. A**zero error**may result in a systematic uncertainty.

Updated: 28th November 2019