The new Thomson Reuters iPhone app from the folks at Reuters Labs is really great. It has easy and fast access to a huge collection of Reuters information from around the world. Also, you can read news offline, which is helpful for iPod touch owners like me. But, there is one irksome design issue, at least for visualization fans like me.
It has a charting tool to review the history of financial indices. At first glance, it seems really slick. InfoVis for the iPhone! Yay! However, when you actually play with it, you realize that as you scan time, the y-axis is constantly changing. This does not allow for true visual comparison between different time periods. The scale should be set to fit the data for all the available time periods, then panning would not be so disconcerting. An option to zoom in or locally optimize the scale could be provided.
Check out the elastic y-axis on this video. I've noted three different y-values that all appeared at roughly the same height as I scanned the data. Also, the bottom of the y-axis is set to maximize the visual variance in the time period. This means that in the example in the video, the y-axis origin is at about 8,000. This helps a viewer to understand the local variance, but exaggerates the overall impression of variance. Whether this is a good idea depends on the task. I guess most financial analysts are interested in recent history, but it would be nice to be able to zoom out to a zero-origin as a sanity check on relative fluctuations.