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,

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,