According to the Constitution of India, the election of the President and the Vice-President is to be held in accordance with the system of proportional representation by means of single transferable vote and the voting at such elections is by secret ballot. 

Proportional representation is an electoral system in which the distribution of seats corresponds closely with the proportion of the total votes cast for each party. Ex- if a party gained 20% of the total votes, in a perfectly proportional system they would allowed to gain 20% of the seats.

The single transferable vote (STV) is a voting system designed to achieve proportional representation through ranked voting. 

Under this system, an elector (voter) has a single vote but with multiple graded preferences. 

The elector can indicate preferences with the appropriate numerals against the names of candidates printed on the ballot paper. 

The vote is initially allocated to the most preferred candidate, yet each one vote has the potential to carry over through multiple counts, depending on the election or elimination of candidates. 

The process of redistribution/transfer of surplus votes from elected candidates and of the votes of the least successful candidates continues until the required number of members (which is one in the case of the President and one in the case of the Vice-President) is elected or reach a quota of votes needed to be a winner.

Because votes cast for losing candidates and excess votes cast for winning candidates are transferred to voters’ next choice candidates, the single transferable vote (STV) is said to minimise wasted votes.