COMPARISON OF HORIZONTAL ERRORS

WITH AND WITHOUT SELECTIVE AVAILABILITY

When SA was turned off in May 2000, GPS measurement of position significantly improved. SA, or Selective Availability, was the intentional degradation of the SPS, or Standard Positioning Service, navigation data in order to deprive a military adversary of real-time more precise positioning.

The plot below compares a day with and without SA using the same GPS receiver.

Actually such a plot as the above is misleading as one cannot see the point plotted on top of each other. The plot and embedded table below show that the difference is much greater than the above plot might make one think.

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