So, Tom Scott planned this down to the second.<br><br>Also: Queues are great example of imperfect progress bars. Suddenly there is someone whose card don't work, or is in the card-only line despite paying in cash. Or therer is problem with scanning the price of a goods, or the discount that they thought was applicable is not, so they have to make a return.<br><br>Progress bars are messy, and so is reality.