Hey Ahsan,

Your question is open ended. I'm assuming that you are referring to a handheld gps. What to look for in these units is WAAS technology, and the version of NMEA. These usally ensure an accurate Lat/Long reading. If you would like i can send you some more detailed information about the technology including air interface messaging, and FCC standards. Let me know. -Z-

I believe the question was:

Anyone know anything about GPS systems? In particular Garmin 3600 series?

Yes, in my field GPS units are used a lot. I also have an interest in the technology. What is your question?