Calculation of increment.

For the purposes of this Act, the increment shall be deemed to be the amount by which on the date of the declaration of intention to make a scheme, the market value of a plot included in the final scheme estimated 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 improvements contemplated in the scheme: 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.