26. I have heard that I can improve my results by applying the "precise" orbits? Where can I find these orbits?

The "Broadcast" orbit (navigation file) information is sent by the satellites. Since the satellite's clock may be off by as much as 7 nanosecs, its position could be off as much as 210 cm. The precise orbit is calculated after the fact by several analysis centers around the world ( the National Geodetic Survey has its own analysis center located in Silver Spring, MD). A combination of the precise orbits yield a global precise called the IGS orbit and is good to less than 5 cm.