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Brennan Center Overview of Voting Equipment

This is the Brennan Center’s resource page describing different categories of voting equipment.

Published: May 31, 2018

Optical/Digital Scan Paper Ballot Systems require voters to mark paper ballots, which are subsequently tabu­lated by scan­ning devices (“scan­ners” or “scan systems”). The scan­ners optic­ally or digit­ally sense the mark­ings on the inser­ted ballot and these marks are used for tabu­la­tion.

Gener­ally, voters select the candid­ate of their choice on optical/digital scan paper ballots by filling in an oval (on ES&S, Domin­ion, Premier/Diebold and Unisyn ballots), complet­ing an arrow (Sequoia ballots), or filling in a box (Hart Inter­civic ballots). These formats are considered tradi­tional paper ballot formats. As complet­ing-the-arrow ballot formats have had higher rates of resid­ual votes, and substan­tially higher rates of over­votes, they should be avoided in favor of “complete-the-oval” ballot formats. 

Once marked, ballots may be scanned on optical/digital scan systems in the polling place (known as “precinct count”) or collec­ted in a ballot box or other­wise cent­rally aggreg­ated, e.g., vote-by-mail ballots, to be scanned at a cent­ral loca­tion (known as “cent­ral count”). Precinct count scan­ners must provide voters notice of over­votes (where voters select too many candid­ates, thus spoil­ing the ballot for that contest) and should auto­mat­ic­ally return over­voted or other­wise erro­neous ballots to the voter for correc­tion. Cent­ral count scan­ners, gener­ally used for mail ballots, do not have this func­tion­al­ity as the voter is not present when the ballot is scanned for tabu­la­tion purposes. 

Examples include:, Domin­ion ImageCast Models Precinct, Evol­u­tion and Cent­ral; ES&S Models 100, 150, 550, and 650; Sequoia-branded and ES&S-branded Optech III-P Eagle; Sequoia Optech Insight and Optech 400C; Premier/Diebold (Domin­ion) Accu­Vote-OS and OSX; and Unisyn OVO.


Ballot Mark­ing Device (“BMD”) systems produce a marked ballot (usually paper) that is the result of voter inter­ac­tion with visual or audio prompts provided by a compu­ter­ized inter­face. The result is a voter-veri­fi­able ballot that may or may not be access­ibly veri­fied. These systems are most often used in combin­a­tion with the optical/digital scan systems discussed above.

Some BMDs produce a paper ballot that uses a tradi­tional paper ballot format. Other BMDs produce a paper ballot that simply includes a list of the voter’s choices and a QR code or a bar code, but is not prin­ted in a tradi­tional ballot format and does not include human read­able mark­ings. For both, voters take the ballot and separ­ately insert the ballot into a scan­ner. For tradi­tional paper ballots, the scan­ner uses the human-read­able marks on the ballot to tabu­late votes. If the ballot includes a QR code or a bar code, the scan­ner uses these marks to tabu­late votes. States that certify code-gener­at­ing BMDs should also mandate that, if the ballot includes a QR or a bar code, it must also include a human-read­able list of selec­tions, and that only the human-read­able portions of these ballots may be used during audits and recounts. These require­ments will ensure that each vote is prop­erly tabu­lated as cast and that errors in the program­ming of the BMD’s code gener­ator or the scan­ner tabu­la­tion system are detec­ted. 

Still other BMDs count votes intern­ally (as do DRE systems) and may save voter selec­tion inform­a­tion. For any BMD that does count, save, or use cryp­to­graphy or other tech­niques to make it diffi­cult to insert fraud­u­lent ballots prepared on other devices (before, during or after actual voting), any discrep­ancy between records stored within a BMD and phys­ical ballots produced would provide clear evid­ence of malfunc­tion or fraud and initi­ate an invest­ig­a­tion to determ­ine the source of the discrep­ancy and the invalid ballots, whether elec­tronic or phys­ical. Examples of BMDs include: Auto­Mark and Populex.

There are many reas­ons a juris­dic­tion will want to purchase ballot mark­ing devices, but among the most import­ant is federal law.  Every polling place that uses optical scan equip­ment must have at least one BMD that allows voters with disab­il­it­ies to vote inde­pend­ently and privately, as other voters do.

BMDs offer many useful features beyond satis­fy­ing federal require­ments to accom­mod­ate voters with disab­il­it­ies. By offer­ing a “read-aloud” feature, BMDs enable voters with limited read­ing skills in the ballot language or visual impair­ments to have the ballot read to them on head­phones. BMDs are also able to effi­ciently provide ballots in altern­at­ive languages. In addi­tion, BMDs can improve the accur­acy of voters’ inten­tional mark­ings on paper ballots, includ­ing elderly voters and those with hand tremors.


Direct Record­ing Elec­tronic (“DRE”) voting systems directly record, in elec­tronic form, the voters’ selec­tions in each race or contest on the ballot. Typical DRE machines have flat panel display screens with touch-screen input, although other input tech­no­lo­gies have been used, such as push-button. Such systems can be compared with mech­an­ical lever voting machines which directly record votes on mech­an­ical coun­ters inside the machine.

The defin­ing char­ac­ter­istic of DRE machines is that votes are captured elec­tron­ic­ally and stored in that form. Such machines may print a durable paper record of the votes cast, for example, after the polls are closed or on an internal printer, but this record is not subject to voter veri­fic­a­tion. DRE machines also record Event Logs giving the time of each signi­fic­ant oper­a­tion on the machine, such as when it was set up for an elec­tion, when the polls were opened, when the polls were closed, and when a ballot was cast (but not which ballot was cast). At the close of polls, vote totals, the Event Log, and all votes cast may be prin­ted. In

addi­tion, elec­tronic records of these may be extrac­ted from the machine (for example, on remov­able media such as disks or compact elec­tronic memory modules), or the records may be trans­mit­ted elec­tron­ic­ally to a vote collec­tion center (for example, by modem).

Proced­ures for using these altern­at­ives vary from juris­dic­tion to juris­dic­tion. Typic­ally, the elec­tronic trans­mis­sion or the elec­tronic memory module is delivered to a cent­ral vote-count­ing system (for example, in the county elec­tion headquar­ters), where juris­dic­tion-wide totals are computed. There are three subtypes of DRE machines, based on the style of user inter­faces/inter­ac­tion:

1. The scrolling DRE uses a touch-screen to collect user input (when not in an audio ballot mode) and typic­ally allows voters to page through separ­ate screens for separ­ate offices. Examples include: Sequoia AVC Edge, the ES&S iVotronic, Premier/Diebold (Domin­ion) Accu­Vote-TS and -TSX, AVS WinVote, and.

2. The full-face DRE has no paging, and it gener­ally involves an elec­tromech­an­ical human inter­face, which uses switches provid­ing tact­ile feed­back to the voter. (The Avante DRE does produce a full-face ballot that uses a touch-screen) Examples include: Sequoia AVC Advant­age and Dana­her Shouptronic/ELEC­Tronic 1242.

3. DREs with off-screen mech­an­ical control allow the user to view options displayed on a screen but provides input via buttons, switches, dials or other input devices. Examples include: Hart Inter­Civic’s eSlate.


DREs with Voter-Veri­fi­able Paper Trails (“DRE w/ VVPT”) capture voter choices intern­ally in purely elec­tronic form and contem­por­an­eously on paper in a record that can be veri­fied by the voter. The paper record is usually not phys­ic­ally handled by voters, and it remains at the polling place, mech­an­ic­ally stored

within or near the DRE machine used to cast the vote. DREs w/ VVPT include those that ensure voter privacy by auto­mat­ic­ally separ­at­ing and random­iz­ing vote selec­tions for stor­age and those with reel-to-reel designs. Examples include: Domin­ion ImageCast X and Accu­Vote TSX; ES&S iVotronic; and Sequoia AVC Edge.

DREs without VVPT do not create a tangible phys­ical record of the voter’s selec­tions on a phys­ical ballot.