I want users of my application to perform 5 exercises a day. I'd like to have a GUI element which shows their current progress, which can be 0,1,2,3,4 or 5. I thought about using something like a progress bar build of 5 squares arranged horizontally, or something like a pie-chart with 5 wedges. The problem is that none of this metaphors seems to be obvious when the progress is 0%. In other words, if you see 5 wedges of the same color it is not obvious if the value is 0% or 100%, or if this is even a progress bar at all!
I've come to realization that cellphones have similar problem when they have to display that battery is discharged: AFAIK iPhone shows 1% in this case, Windows Phone shows heart symbol inside battery. Also when the battery is discharged and I start to charge it, then my Android shows an animation, and Windows shows a thin red line at the bottom of the battery (something like the 1% trick).
So perhaps this is a good idea, to display 0% as 1%, just to make the distinction between "done" and "todo" areas obvious?
I also considered the most obvious solution, that is to use numbers and/or text. But then again: is there any reason for using progress bars instead of numbers? I think there is.