The memory card is very simply a programmable memory device with a battery backup. The Accu-Vote accesses this memory directly. If something goes wrong when the Accu-Vote is writing new data to the memory card or if the Accu-Vote crashes (as computers have been known to do) and writes to random memory locations, then the data on the memory card may be corrupted (nasty word I know but it fits). All this means is that the data is modified in an unintentional manner. This could also happen without an Accu-Vote through static discharge or some types of radiation (i.e. old airport scanners, cosmic rays???).
There are several mechanisms that we could use to detect this. We use the simplest of these which is to treat the data as a series of numbers and store totals of sets of those numbers as separate data known as checksums. If the data has been modified without updating the checksums, then the checksums will fail to add up.
The Accu-Vote keeps three different types of checksums for three different classes of data. These are text, counters, and precinct. The text checksums cover all the titles and names that are used mostly just for printing reports. Since the text data does not affect the other operations, we check it only occasionally and we allow most operations to continue after a warning.
The counters and precinct data are considered critical and the Accu-Vote is largely inoperable when these checksums fail. We do support the option to clear the counters if only they have been affected and then counting may be restarted. However there is no way to recover from corruption of the precinct data other than to clear and re-download the memory card.
All checksums are validated upon insertion of a memory card or at power on. Thus this is the most common time to detect problems. However the counter and precinct checksums are validated every time a new ballot is scanned. If an error is detected, counting is aborted.
Now to Lana's questions. The above should answer everything other than why erroneous data managed to upload. I see two possible explanations. One is that the data was corrupted after the checksums were validated. In this case the errors would show the next time the checksums were checked. The other possibility is the miniscule chance that the erroneous data managed to add up to the correct checksum. The checksums are stored as totals ranging from 0 to 65535 so the chance of this happening are less than 60,000 to 1 just based on that. Other factors add to this to make it extremely unlikely. However in this case the card would not later show checksum errors.
So John, can you satisfy Lana's request from this? I can't without more details.
John McLaurin wrote:
Please see below and let me know what you think. Tab, one of these issues
we discussed - it's the one were we printed the audit report showing the
check sum error and the poll worker restarting the unit.
Please let me know what you guys think.
From: Lana Hires [mailto:email@example.com]
Sent: Wednesday, January 17, 2001 8:07 AM
To: firstname.lastname@example.org; Glanca@ges.com
Cc: Deanie Lowe
Subject: 2000 November Election
Hi Nel, Sophie & Guy (you to John),
I need some answers! Our department is being audited by the County. I have
been waiting for someone to give me an explanation as to why Precinct 216
gave Al Gore a minus 16022 when it was uploaded. Will someone please
explain this so that I have the information to give the auditor instead of
standing here "looking dumb". I would appreciate an explanation on why the
memory cards start giving check sum messages. We had this happen in several
precincts and one of these precincts managed to get her memory card out of
election mode and then back in it, continued to read ballots, not realizing
that the 300+ ballots she had read earlier were no longer stored in her
memory card . Needless to say when we did our hand count this was
Any explantations you all can give me will be greatly appreciated.