Point elasticity is brought in use when the change in price is quite small, which means. The two points between which elasticity is being measured or calculated essentially collapse on each other. Differential calculus is used to calculate the instantaneous rate of the change of quantity with respect to changes in cost
(dQ/dP) and after this it is multiplied by P/Q, where P and Q are the coat and quantity obtaining at the instant of interest. The formula for point elasticity can be given as:
? P Q
Or this formula can also be written as follows:
d P Q
Where d = infinitely small change in cost.