1.1.2 Classification of measurement
(1)According to the principle of measurement,it can be classified into direct measurement and indirect measurement.
Direct measurement refers to a measurement in which an object is measured by direct comparison with the instrument without auxiliary calculation.For example,weighing mass with a balance,measuring length by using a meter ruler,measuring time through a clock,etc.
Indirect measurement means a measurement in which a value is calculated by using one or several physical quantities through the given function relations.
(2)Classification based on the frequency of measurements(https://www.daowen.com)
Measurements can be classified as single measurements and multi-measurements.Specifically,multi-measurement is categorized as equal precision repeating measurement and unequal precision repeating measurements.
Single measurement means that one physical quantity is measured for only one time.For example,the specific heat capacity of solid or liquid can not be measured for more than once because the equilibrium temperature passes in a moment.
Equal precision multi-measurement means that the same measurer with the same instrument and method,in the same environment,measures the physical quantity several times repeatedly to take the average as the result.
Unequal precision multi-measurement means that in the measurement of the same physical quantity,if one or several factors(instruments,methods,operators,external conditions,etc.)have changed,the accuracy of measurement would alter.The weighted average value of each measurement is taken as the result.Usually,the single measurement and equal precision multi-measurements are adopted in experiments.
