Chapter #58. Show a Numeric Progress Indicator on the Progress Bar
Show a numeric (percentage) indicator on the progress bar, but only if there's time to read it.
A progress bar and a number that appears for a fraction of a second is just confusing and adds to the visual clutter that the user needs to process. If they're going to be stuck looking at the progress bar for a few seconds, then a percentage is a nice, universally-understood way of keeping them updated.
Also, this numeric indicator could be an amount of time. So, for an update, you can show a certain amount of minutes remaining. However, a percentage is more useful for shorter processes. Be careful because calculating "time remaining" is often a big technical challenge. It's pretty common to see an update say "24 minutes remaining" and then see it complete in the next few seconds. If you're not confident that you're giving users an accurate time, then it's better to leave it out and use a percentage...