The closest United States Senate election in history occurred in New Hampshire in 1974. A contest between John A. Durkin, Manchester and Louis C.Wyman, Manchester was recounted several times by the State of New Hampshire and by the US Senate with differing results. The turnout for that special election was greater than in the original election. One problem revealed by this recount was the need for uniform, secure ballot boxes, which are now provided by the state. Recounts have to be done by human beings because marks may be misaligned.
All ballots are paper so they can be recounted if necessary.
The old-fashioned kind that is marked with an x and counted by hand. The accuvote system where you fill in an oval. The op-tec system where you fill in the gap in an arrow. Mr. Gardner pointed out the problems with punch card voting before this system became widespread in New Hampshire. The punch card system became available in the 1970s and was cheap.