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Comment by dalek2point3 | Hacker News Reader

Very interesting. Actually, something similar happened in the US back in 2000, when Clinton turned off something called "Selective Availability" in the US. This program deliberately degraded civilian GPS signals. After SA was turned off, we went from a GPS system that was accurate to a football field-type area to one that is accurate to a tennis-court ish area.

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I don't understand these units of measurement. Football-field GPS was 4 times less accurate than tennis-field GPS? your reference indicates that uncertainty was 45 meters and became 6.5 meters, one order of magnitude improvement.

To continue with mixed standards -- a tennis court measures 23.78 by 10.97 meters (78 by 36 feet, I'm surprised it hasn't been metrified). The Japanese system should be about 3 orders of magnitude more precise than tennis-court-rated GPS.

Wolfram Alpha says:

  area of an NFL football field in square meters: 5351m^2
  area of a circle of radius 45 meters: 6361.73m^2

  area of a tennis singles court in square meters: 196.7m^2
  area of a circle of radius 6.5 meters: 133m^2

It's pretty close.

(A volleyball court would be closer at 162m^2.)

So, table tennis table? Chess board?

This is nothing like turning SA off. SA was the intentional injection of pseudorandom data to degrade GPS accuracy in order to deny enemies accurate positioning data. This is a system of satellites launched to augment GPS signals in a certain area of the globe for advanced civilian positioning applications.

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