http://www.cs.uiowa.edu/~jones/voting/colloq/
Jones Talk, Slide 6

A Brief History of Voting Technology

• Optical Mark-Sense Ballots
  -- First use, early 1970's.
  -- Growing use through 1990's.
  • Essentially a modified Australian ballot.
  • No ballot marking fixture required, just a pencil.
  
  -- Weakness: Discrimination between votes and smudges.
  -- Weakness: How do you make the voter use the right pencil.
  -- Weakness: Mark sensing threshold variation versus voter intent.

  All physical ballots have a marginal mark problem. Interpreting marginal marks always raises subjective issues.

  -- Strength: Recount is possible.
  -- Strength: Machine count is fast and can be very accurate.