Explained: Symbol Loading Unit (SLU), the ‘matchbox’ that feeds EVM candidate information

What is a Symbol Loading Unit (SLU) and how does it work?

Symbol Loading Units (SLUs) were introduced around the same time as VVPATs — a little over a decade ago. VVPATs help voters verify their votes — they see a slip with a printed image of the party symbol they voted for.

How SLU works.

But for the VVPAT to print a symbol correctly, information pertaining to the list of candidates and their symbols must be loaded on to the VVPAT machine in the correct order. This is where the Symbol Loading Unit, or SLU, comes in. In fact, the introduction of VVPATs necessitated the use of SLUs.

The SLU is used to load the symbols of the candidates onto the VVPAT. It is a matchbox-sized device that is first connected to a laptop or personal computer, from where a symbol loading application is used to load a bitmap file containing the candidates’ names, serial numbers, and symbols.

The SLU is then connected to the VVPAT to transfer that file on to the paper audit machine. This is done under the supervision of a district election officer.

At which point in the election process are SLUs used?

The SLUs come into the picture only a few days before polling in a particular seat, when the EVMs are being commissioned and the list/ order of contesting candidates is decided and set on the ballot unit (the machine where you press the button to vote) and the VVPAT (which produces the paper audit trail of your vote).

Candidate-setting can happen at any time from five to two days before voting at a seat. Once the SLU is used to load symbols onto the VVPAT, the EVM is ready for use. After this, the SLU is of no relevance to the actual voting process.

What happens to an SLU after symbols are loaded?

Typically, a small number of SLUs are enough to load symbols onto all VVPATs for a seat. According to EC officials, it takes an SLU two to three minutes to load each VVPAT.

Once the symbol-loading is complete, the SLUs are handed over to the concerned district election officer for safekeeping. They remain in the officer’s custody until the day after voting. Afterward, the SLUs are released to the engineers of the two EVM manufacturers, Bharat Electronics Ltd (BEL) or Electronics Corporation of India Ltd (ECIL), so they can be used to load symbols onto VVPATs for other seats in subsequent phases.

Thus, in a multi-phase election like the ongoing one for the 18th Lok Sabha, an SLU is typically reused after one phase of polling to load symbols onto VVPATs meant for other seats in subsequent phases.

What has the SC said about the SLUs?

The court has said that the SLUs should be sealed and stored immediately after the symbol-loading process for a seat is complete. It must be stored for a period of 45 days after the declaration of results, so that it can be opened and examined like EVMs in case of an election petition.

This effectively means that an SLU used for loading symbols onto VVPATs for one seat can no longer be reused for other seats. Consequently, the EC will need more SLUs. Sources said the Commission currently has about 5,000 SLUs, and will need an additional 2,000 to implement the SC’s direction.

And what has the top court said about microcontrollers?

In an unprecedented move, the court has allowed candidates to seek verification of EVM software. This effectively means that a candidate can ask ECI officials to check the one-time programmable software in the BU (Ballot Unit), CU (Control Unit), and VVPAT for tampering, in case of any doubts regarding the result.

This verification involves inspecting the burnt memory/ microcontrollers of these three components. The court has proposed a formula for doing this: engineers from the EVM manufacturers will conduct checks on 5% of the EVMs per Assembly constituency or Assembly segment of a parliamentary constituency. Candidates must submit a written request within seven days of the announcement of results, and will have to bear the expense of the process.

This right to seek verification, however, is limited to those candidates who come in second or third. Engineers from the manufacturing companies will certify the authenticity and intactness of the memory/ microcontroller.

What happens if the microcontrollers, upon verification, are found tampered?

The court has only said that if any tampering is found, the candidate will be refunded the cost of verification. It has not said how the election result will be impacted.

What changes on the ground?

Nothing changes for the voter. However, a lot changes in the way the ECI organises polling.

The ECI will now have to store SLUs for 45 days after voting. To reserve one SLU exclusively for one seat, it will need to order more SLUs. It will also have to ensure the verification of EVMs upon request from candidates who finish second or third, which may require additional manpower.

Also, the ECI will have to examine whether the Representation of the People Act of 1951 has to be amended. The election law currently states that an election petition challenging a result can be filed in court by a candidate within 45 days of the declaration of results. During this period, the EC machinery does not touch the EVMs. If these machines now need to be unsealed for verification purposes, the poll panel will have to determine how this can be accomplished.