Fairness and digital parking meters

As those who have used them have probably noticed, new digital parking meters have liquid crystal displays which, upon insertion of money, begin to count down to 0:00, at which point the display gives some sort of signal to meter-people that it is expired. Sometimes this is in the form of little circles under the display that turn from green to red, and sometimes the display actually flashes red itself. At this point the meter is considered expired, and one is fined a flat amount no matter how long one is away from one's car after this.

The only justification I can think of for the obvious unfairness of this flat fine is the fact that the meter reader, and therefore the city or corporation fining you, doesn't know how long it's been since you meter's run out. So here's my question: Why don't digital parking meters keep counting below 0:00? I think they should display negative time on the screen. That way, they can ticket you based on the amount of time you went over. If ones car sat for five minutes beyond the time paid for, they might be charged a few dollars, while someone who parked for five hours without paying would get a thirty or forty dollar ticket.

How would this affect the usage of the meter? Not much. Just like now, you would park, get out of your car, and walk up to the meter. It would probably have a negative number on the screen. However, as soon as you inserted any money, the screen would read just as it does now: 0:00 plus the amount of time payed for. Then, if you were gone for longer than you expected, you would be fined based on the amount of time between your meter running out and the meter-person checking it.

The way that we meter parking spaces now is a holdover from the days of meters that actually had dials and were limited to a range from 0:00 to some arbitrary maximum. Owners and manufacturers of digital meters should put this technology to its full use and charge more fairly for expired parking.