hriessen - 6/19/2009 09:30 It is not a dumb question. Matter-of-fact, it is a very relevant question. From any well surveyed base station (= using one base station for the correction signal), one-inch accuracy can be expected up to 6-8 miles away from the base station depending on weather, GPS-satellite constellation, equipment, etc. When operating further from the base the accuracy declines to about 2-2.5 inches at 20 miles. I would not recommend to go much further. Above 25 miles the RTK-fixed acquisition time can become a problem on some days. Outside a CORS network using a network solution (= using multiple base stations for the correction signal) it is still possible to acquire good accuracy. Roughly, you'll see the same decline in accuracy as with a single base station solution. The problem usually becomes getiing the correction signal to the rover. The standard 900 MHz radio is not the best way to maintain contact with the base. It will be OK for short distances or, if the antenna is raised, for the medium distances. Most likely you'll still need a repeater to bend the signal around treelines and buildings. The 450 MHz radio will be a little better, but requires a license. The best way the transmit the correction signal will be the use of cell phone signal. Ofcourse this requires this signal is available in all your fields.