I should have explained this a long time ago

The 2 lines below are simulating a download speed indicator as would be shown in a browser, the difference is the first line is using proportional numbers (The default, since it’s a proportional font, by default), so the speed indicator following it slides around as the speed varies. The second row however is using tabular (aka. fixed width) numbers, so as long as the amount of digits is unchanged, the overall width of the text remains unchanged, and the speed indicator is stable and never slides back and forth.