The SPS is provided on the L1 broadcast frequency and more recently the L2 (see Section 13.3) at no cost to the user. This service was initially intended to provide accuracies of 100 m in horizontal positions, and 156 m in vertical positions at the 95% error level. However, improvements in the system and the processing software have substantially reduced these error estimates.
The PPS is broadcast on both the L1 and L2 frequencies, and is only available to receivers having valid cryptographic keys, which are reserved almost entirely for DoD use.
This message provides a published accuracy of 18 m in the horizontal,and 28 m in the vertical at the 95% error level.