If you’ve spent any time at all on Internet message boards, you’ve probably seen the same question asked over and over again. On computer message boards, a common question is “Why do the progress bars (meters) in Windows suck so much?” You’ve probably dealt with this yourself: you want to move a file from one hard drive to another on your computer, so you do the drag and drop thing, and Windows’ progress meter appears… “2 minutes remaining”. It then inexplicably jumps up to “38 minutes remaining” for a minute or two, then drops back down to “45 seconds remaining” before jumping back up to “1 minute remaining”. A similar thing sometimes happens when you’re installing software: the progress meter will slowly move up to, say, “38% complete”, and then stay there for a couple of minutes before suddenly jumping up to “75% complete”.
What’s the deal? Well, the snarky answer is that “your computer can’t predict the future”. The longer answer is the same, only slightly more involved.
Let’s say that you have a GPS system in your car. You’re sitting in downtown Charlotte, NC and want to drive to an address in downtown Atlanta, GA. You enter the address into the GPS unit, which immediately gives you an estimated drive time of 3 hours and 25 minutes (which is based the current distance you want to drive divided by 55mph). So you start driving to the address, and the estimated drive time slowly starts ticking down… “3 hours, 15 minutes remaining… 3 hours, 5 minutes remaining… 2 hours, 55 minutes remaining”. As luck would have it, there’s a massive wreck just outside of Greenville, SC. You’re stuck in bumper-to-bumper traffic and are doing around 2mph. Suddenly the estimated drive time jumps up to “16 hours, 47 minutes remaining”. As you creep along, the drive time keeps getting longer: “18 hours, 2 minutes”. You finally clear the wreck, and you figure that all the local cops are busy dealing with the accident… so you floor the gas pedal. Once you hit 125mph, the estimated drive time plummets to “45 minutes remaining”. Your road rage subsides after a few minutes, so you lay off the gas and settle in at a more reasonable 70mph. The estimated drive time is now back to a more normal “1 hour, 25 minutes”.
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