from:
http://www.fankhausers.com/articles/tabulation.htmlThe punch-card systems use standard, readily understood hardware. The equipment used for tabulation in the punch-card system was well known to computer professionals and easily interchangeable. Tabulation software ran on an industry-standard PC that could easily be replaced on short notice. The card reader was standard enough that a replacement could easily be brought in. Wayne County added a margin of security and integrity to their system by acting as a "depot" for a spare card reader in this region, thus having two interchangeable independently tested card readers on hand. The result of this from a testing point of view is that there was no way to tamper with the equipment to affect results because a different computer or card reader might be substituted at the last minute to run with the previously tested software.
The open hardware architecture allowed thorough testing to occur. Testing of the punch-card system began several weeks before the election was scheduled to take place. Our vendor (ES&S) would send us a copy of the parameters that configured the tabulation program for the next election. The program with the parameters loaded was tested in the presence of the local election board, interested members of the public and press, and two "computer experts" observing the tests on behalf the two major parties. This test involved a standard "test deck" of cards designed to cast a different but predictable number of votes for each candidate. In addition, the observers would add a few "trick cards" to the deck to make sure the correct results, although known to the observers, would be unknown in advance by either the programmers or operators of the equipment.
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Untested software was never used. Once the test had completed, both the program and the parameters (on standard disk) where then sealed in a lock-box along with the test deck in the presence of the observers. On election night, the observers might ask that the program or parameters be reloaded from the sealed disks to ensure that nobody had replaced the program in the computer in the meantime.
In addition, on election night, the same test deck used for the earlier tests was used to run a pre-tabulation and post-tabulation test on election night. Again, if they wished, the observers could throw a few "trick cards" into the deck at this point.
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Does not seem like the process is invulnerable to manipulation, just that the punch cards are evidence in the event of a hand recount.