Accuracy and Consistency in Measurements
1. ___________ of a measurement is how close the value of a measurement
to the ____________ value.
2. The level of accuracy is related to the relative error.
3. An error is a between the measured value and the actual
4. Accuracy can be improved by : -
(a) repeated readings are taken and the average value is calculated
(b) avoid parallax errors
(c) avoid zero errors
(d) use measuring instruments with a higher accuracy.
For example, a vernier callipers is more accurate than a ruler
1. / Precision of an instrument is the ability of the instrument
to measure a quantity with little or no deviation among measurements.
2.. A measurement is considered consistent will have a relative
deviation or no deviation from the average value .
3. A deviation is a difference between a _______________value and its
average value .
4. average deviation = Total deviation
number of value taken
5. relative deviation = average deviation x 100 %
6. Consistency can be improved by
(a) eliminating parallax errors
(b) exercising greater care and effort when taking readings.
(c) using an instrument which is not defective.
7. Comparisons between consistency and accuracy by considering a target.
A student used vernier callipers to measure diameter of a glass rod. The table below shows the readings.
Relative deviation = ( 0.01 / 2.242) x 100%
= 0.45 %
1.4.3 Sensitivity in Measurements
1. Sensitivity of an instrument is its ability to detect a small change in the
quantity to be measured.
2. A measuring instrument that has a scale with a smaller divisions is more
3. Measuring instruments.
Errors in Measurements
1. An error is the difference between the measured value and the actual
2. There are two main types of errors in measurements,
A. systematic errors
B. random errors.
A. Systematic errors
i. The error in calibration of instrument which makes the instrument
defective. (We must examine the instrument carefully before using
ii. ________ error which means the pointer of the instrument does not
return to zero when not in use. ( Zero error can be corrected by
compensating the readings)
iii. A problem which persists throughout the experiment such as
repeated error in reaction time and wrong assumption.
Systematic errors will lead to decrease in
B. Random errors
i. Arise from unknown and unpredictable variations in condition, and
will produce a different error every time you repeat the experiment.
ii. May be due to:
(a) personal error (human limitations of sight and touch)
(b) lack of sensitivity ( instrument does not respond / indicate
insignificant or small change )
(c) natural errors ( wind , temperature, humidity, refraction, magnetic
Field or gravity )
(d) wrong technique ( applying excessive pressure when
turning a micrometer screw gauge )
iii. Can be minimized by repeating the measurement several times
and taking the average (mean) of the reading .
iv. Parallax error
An error in reading a measurement because an observer’s eye and
the pointer are not in a line perpendicular to the plane of the scale .
(the eyes of the observer must be align and perpendicular to the scale of