For the first time in India's parliamentary elections, the country's Election Commission will undertake exercise of matching EVM results with Voter Verified Paper Audit Trail (VVPAT) machine slips during vote-count of the ongoing polls on May 23.

The polls body said that in case of a mismatch between EVM (Electronic Voting Machine) and VVPAT machine counts, the latter will be held valid, reports our New Delhi correspondent.

The exercise of matching EVM results with VVPAT slips was earlier held in various state assembly elections.

Citing rule 56 D (4) (b) and 60 of the Conduct of Election Rules, a senior EC functionary said instructions have been issued to all state chief electoral officers that in case of a mismatch between the result displayed on the control unit of electronic voting machine and the manual count of slips generated by the VVPAT, the slips will be recounted until the tally matches either the EVM result or one of the previous VVPAT slip counts and this will be taken as the final number.

According to the Indian EC, no mismatch has been reported since the practice of cross-checking votes was introduced in state-level elections.

As the Supreme Court made it clear on Tuesday that random matching of VVPAT slips with EVMs will take place in five polling booths per assembly segment in each parliamentary constituency, the exercise will be held in 20,600 of the 10.35 lakh polling stations on May 23. On an average, a parliamentary constituency comprises eight assembly segments (constituencies).

So far, paper audit trail checks had been done in only one polling station per assembly segment selected randomly by a draw of lots though the VVPAT machines are deployed in all the polling stations.

A top EC official said that it used to take one hour when slips of one VVPAT machine were counted in one polling station per assembly segment. "Four additional VVPATs will take on an average four additional hours to count," he said adding that the official results would, therefore, take at least four more hours to be declared.

India has 543 parliamentary seats and 4,120 assembly seats. Now, multiplied by five, the paper audit trail checks will take place in 20,600 polling stations spread across these assembly seats.

"The number of voters vary from 800 to 2,500 per polling station," another functionary said.

For this year's parliamentary polls, the EC has set up nearly 10.35 lakh polling stations across the country as compared to nearly 9.28 lakh during the previous national poll in 2014, an increase of 10.1 per cent.

Nearly 39.6 lakh EVMs and 17.4 lakh VVPAT machines are being used in these polling stations. These include reserves. One control unit and at least one ballot unit where buttons are placed constitutes an EVM.

VVPAT machine is a device which dispenses a slip with the symbol of the party for which a person has voted. The slip appears on a small window for seven seconds and then drops in a box.

The penultimate phase of polling in India's current national poll will be held on May 12 and the final phase on May 19.