Edward Tufte: Sparklines: theory and practice
edwardtufte.com
edwardtufte.com
When you don't have a fram of reference, it can be hard to tell what directions the lines are moving. You end up with an effect like this illusion: http://www.internetgamesfree.com/games/images/illusion_68.gi... where your perception of the line deviates from reality.
The "normal range" line he shows does a great job to fix this.
If you want to play with sparklines I can really recommend this library - it's very nice to work with and supports lots of different sparklines:
http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0...
For example, do gkrellm's "krells" count as an example of sparklines, or are they something else? --> http://members.dslextreme.com/users/billw/gkrellm/gkrellm0.p...
I would say what you linked to would not be considered sparklines from the above.
Library used: http://key-solutions.ca/cksparkline.html