Explanation:
As an approach to the problem of answering the question:....
"How Many Machinecounted Ballot Batches do we need to Handcount ("Audit"), in order to be reasonably sure we would catch any error in the machinecounting process?"
....we now have a straightforward way of figuring that out.
Citizen activists have cooperated to develop a tool for that estimate.
This can be used in three ways: As background to write Law or Procedures; as the basis for establishing simplified rules; or as the active guidance during the processing of ballots, to decide "when to quit" handcounting.
(With thanks to Kathy Dopp, the Brennan Center, Ronald Rivest and Marian Beddill.)

The Calculator:
There are five independent variables which need to be determined or estimated:
 The whole set  "the NUMBER"  of ballotbatches (precincts, machineruns, etc) for which the jurisdiction is holding the election.
 The Margin between winning and secondplace Candidates, in the initial election results. (How close is the election?)
 Your desired Probability or Certainty Level, for finding one or more corrupt counts. How sure do you want to be? Like, 90% sure? ...or 95%? ...or 99% sure? (higher numbers mean more work.)
 Maximum amount of vote switching, per vote count, that would not be immediately recognized as suspicious. If a fraudster shifted 50% of the votes in one set, would it be noticed by ordinary caution? Clearly yes. But what if they only shifted 15%? Or 3%? In plain english, for this measure of amount of shift, how bold can we guess that a fraudster would be in THIS jurisdiction on THIS race? Another element is how many batches (machines, etc) he would try to fiddle with?
 So, what you need to know, is how many batches should be pulled for a handcounted doublecheck? Those factors above, determine how much effort is worth doing. Since the formulas don't work backwards, you have to input a guess, and this model will tell you if "YES", it was good enough, or "NO", it was not.
Download the spreadsheet (it's a small file):
HowManyToAudit.xls (Excel97),
HowManyToAudit.ods (OpenOffice Calc)
and the version posted by Kathy Dopp, at her website: electionarchive.org
HowManyToAudit.xls (Dopp Excel97)
(we are each tweaking it, headed to settle on the same version.)
