Measurement

Precision

Precision is the ability of an instrument in measuring a quantity in a consistent manner with only a small relative deviation between readings.

Relative Deviation

The precision of a reading can be indicated by its relative deviation.

The relative deviation is the percentage of mean deviation for a set of measurements and it is defined by the following formula:

Accuracy

The accuracy of a measurement is the approximation of the measurement to the actual value for a certain quantity of Physics.

How to Increase Accuracy

1. taking a number of repeat readings to calculate the mean value of the reading.
2. avoiding the end errors or zero errors.
3. taking into account the zero and parallax errors.
4. using more sensitive equipment such as a vernier caliper to replace a ruler.

Sensitivity

1. The sensitivity of an instrument is its ability to detect small changes in the quantity that is being measured.
2. Thus, a sensitive instrument can quickly detect a small change in measurement.
3. Measuring instruments that have smaller scale parts are more sensitive.
4. Sensitive instruments need not necessarily be accurate.

Micrometer Screw Gauge

1. Turn the thimble until the object is gripped gently between the anvil and spindle.
2. Turn the ratchet knob until a "click" sound is heard. This is to prevent exerting too much pressure on the object measured.
   
3. Take the reading.

(This image is licensed under GDFL. The source file can be obtained from wikipedia.org.)

Reading of main scale = 5.5mm
Reading of thimble scale = 0.27mm

Actual Reading = 5.5mm + 0.27mm = 5.77mm

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