Calculation of increment.

For the purposes of this Act, the increment shall be deemed to be the amount by which at the date of the declaration of intention to make a scheme, the market value of any plot with reference to the improvements contemplated in the scheme on the assumption that the scheme has been completed would exceed on the same date the market value of the same plot estimated without reference to such improvements : Provided that, in estimating such values, the value of buildings or other works erected or in the course of erection on such plot shall not be taken into consideration.