Precinct count optical scan (PCOS)

1. Optical scan technology that permits voters to mark their paper ballots within a precinct and submit the ballot for tabulation. Precinct Count systems provide overvote/undervote protection.

Source: Information Technology Terminology, U.S. Election Assistance Commission, https://www.eac.gov/documents/2017/09/21/information-technology-terminology-security

2. Precinct count optical scan (PCOS) units are optical scan voting machines that are specifically designed and used for precinct-based vote tabulation. PCOS units are used in polling places in jurisdictions in 40 states.

Source: America’s Voting Machines at Risk, Brennan Center for Justice, https://www.brennancenter.org/sites/default/files/2019-08/Report_Americas_Voting_Machines_At_Risk.pdf