CBSE Class 11-commerce Answered

All measures of dispersion do not measure variation about some particular value of the series.
Such as range and quartile deviation.
Range measures the difference between the highest and the lowest value of a statistical; series.
Quartile deviation is defined as the half of inter quartile deviation that is the difference between Q3 and Q1.

However, measures of dispersion such as mean deviation and standard deviation are worked out as deviations from central tendency. Firstly, with these methods we can assess how precise is the central tendency as the representative value of all the observations in the series. Secondly, we can assess how scattered are the actual observations from their representative value.