Recount in Elections

In hand counting of voting papers, errors of up to 2% are possible, according to some research. Anyone who has had to count bits of paper in bulk will tell you of some common causes of error - counting the same paper twice, counting two or more as one (they can tick together), losing concentration, etc. Scientists at Rice University and Clemson University compared two methods:

The first procedure, the “read-and-mark” method, utilizes four election officials who count the ballots sequentially as they are taken from the top of an unsorted stack of ballots. One official speaks aloud the choice on the ballot for the race being tallied. Another official observes each ballot to ensure that the spoken vote corresponds to what was on the ballot and also collates ballots in cross-stacks of 10 ballots. The final two members of the audit team record the tally.

The second procedure, the “sort-and-stack” method, is like the read-and-mark procedure but only counts one race at a time. Unlike the read-and-mark procedure, however, the roles and labor needed for the counting task is not divided among the team members. The team is comprised of three members who each have their own tally sheet.

Based on the processing of the ballots, the researchers found a one-half to 1 percent error rate for the “read and mark” method, and up to a 2 percent error rate for the “sort and stack” method.

(Where I work teams count financial papers in bulk and we use the 10-sheet cross stack method, but you still get 1% or 2% errors, but these are only found if we actually do a recount)

As for electronic or mechanical methods, there is much to go wrong also - errors in software, badly adjusted stack counting machines, worn parts, etc.

That's 'they can stick together'.

In addition to what contrex has stated, there can also be the issue of dangling/hanging chads. With those, it's a matter of the voter having marked a selection, but failing to press hard enough to sufficiently loosen the piece of paper (chad). It created a bit of a problem in the 2000 election for President down in Florida.

There are mixed currency counters that are accurate. They should be able to make ballot counter machines that are accurate.

Unhackable. They've been hacked for decades.