8.4

Contamination
The single but critical danger with any implementation that deals with PlanetPress Capture is
"Contamination". Basically, contamination happens when an Anoto Digital Pen writes on a "wrong"
document or is docked in the wrong location. This can happen any number of ways and in different
situations, and can have devastating effects in some of those cases so please pay special attention to this
section.
First, contamination is not limited to implementations that extend their patterns through methods 1) and 2)
above. Any time that a pen writes on a "wrong" document, it is considered contamination. A simple example
in a basic implementation would be to print a document with a pattern on it, put this paper aside (or lose it on
a desk somewhere) and forget about it. Assuming proper processes were put in place, this document would
eventually be closed by a manual or automatic procedure. However, the physical document with the pattern
still exists even if it is closed in regards to the PlanetPress Capture database. Contamination would happen
if a new document is printed with the same pattern, but somehow the "old" document re-surfaces and
someone writes ink on it and docks the pen. When this happens, neither the pen nor PlanetPress Workflow
can understand that the data does not belong on that document and will happily update the "current"
document, possibly closing it. Because the "old" document relates (presumably) to a different client, this
means the "current" document has invalid information.
This can be prevented through simple methods such as printing a date on each sheet and ensuring that
users never sign a document that is older than a certain time, for example 48 hours. These sheets should
simply be destroyed.
Second, contamination can happen in method 1) above if a pen or paper is moved from one location to
another. Similarly to the previous contamination example, if there exists a document in the Capture
Database where the "wrong" data is processed, it will update a document where it does not belong. Again,
neither the pen nor PlanetPress Workflow have any idea that this causes an error until it's too late.
Third, contamination (the most common one) can happen if pattern sequences get mixed up, if pens or
paper gets swapped between users, etc. For example, again using a shipping company (with example 2-A),
if two of the drivers were to meet for a coffee and exchange their pens inadvertently (we hope, anyways), the
pens would be signing the "wrong" documents all day and, when docked, would update the wrong
documents in the database.
In all of these cases, the errors often do not appear when the wrong document is updated - it actually occurs
when the "right" data is processed. This happens precisely because the Pen and Production have no idea
that the wrong data is received and will generally close the document after that "wrong" data has been