While the concept of a %-complete progress bar while installing computer applications or browsing web sites is, in theory, a good idea, the reality is somewhat different.
There’s a fundamental concept that is missing from the %-complete indicator: the unit of measure.
That is, does the progress bar an indicator of the Volume of data, the number of files to be written, or the duration of time expected for the process to finish.
I’ve had users say, “The progress bar in IE is all the way to the right, but there’s still nothing on the page… your system sucks!” Well, in that case, the progress bar is an indicator of time, not volume. That time value can vary depending on different factors.
How about waiting for an application to install–there’s that effing progress bar, scrolling across the page. Just when you think it’s finished, it jumps back to 0%, hoping you didn’t notice. In this case, it’s actually an indicator of the volume of data read or written to the drive for each file, not for the entire program–which, in some cases, may consist of hundreds, thousands, or tens of thousands of files. But it doesn’t say that.
I just spent an hour freezing my ass off in a datacenter waiting for one of those stupid progress indicators to go from 98% complete to 100%. The first 98% went by in about four minutes.
Tip: When you write an application that uses a progress bar, get out your stopwatch and time the process on an “average” computer. Do it a few times and record the highest number. Then, write your code to show the user how much time it’s expected to finish the needed process.