A major failing of sparklines in practice is the lack of a visual benchmark.
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.
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.