Just once in my programming career, I wrote a program to install some software. (In fact, it was one of the toughest types of installation: the video driver for the main CRT.) Every install program shows a progress bar so that you can see how the installation is going. I took this bar very seriously. The files that an install program installs are compressed, but I found that the rate of install progress was directly related to the size of the uncompressed files. I built into my install compilation, the knowledge of how many bytes had to be installed, and I used that figure to produce a pretty accurate and reassuring progress bar.
That is so rare.
I'm, sure you've see progress bars that creep from about zero to fifteen percent; they hover there for awhile and suddenly: bang, the install is done. And you've seen bars that expand from 0 to 100 percent several times during an install, without a clue how many times the bar is going to fill. Having paid my dues here, I'm contemptuous of all these lousy progress bars. If you're going to display one, make it real!
I recently watched a software install that hits a new low. I suspect that the programmer in this case was himself subjected to so many terrible progress bars that he had no idea what they were. During his install, a black smudge moves back and forth on the progress bar, back and forth, back and forth. It doesn't show progress at all; although it does provide some confidence that the installer program has not died. Now really ...