This can be illustrated with the help of an example. Let us assume that, when the price of petrol is measured in rupees/litre, the slope of the demand curve at point A is -0.001 (figure 4.3). On the contrary, when price is measured in rupees/ml, the slope at point ‘A’ becomes -0.000001 as shown in figure 4.4. However, in both cases, price elasticity of demand at point ‘A’ remains the same i.e., -2, irrespective of the units chosen for measuring price and quantity.
Thus, the slope of the demand curve at any point depends upon the units in which price and quantity are measured. The slope of the demand curve at point ‘A’ (in figure 4.3) is much more when price of petrol is measured in rupees per litre, than when it is measured in terms of rupees/ ml (Figure 4.4).
The price elasticity of demand, on the other hand, is completely independent of units of measurement. In other words, it remains unchanged irrespective of the units in which quantity demanded is measured.