This is a great program and the developer is very responsive to any questions I've had. You can download official NOAA charts for free [ http://chartmaker.ncd.noaa.gov/ ] which work perfectly with the program. The usb GPS unit I use is the GlobalSat
BT-359 SiRF Star III Bluetooth GPS Receiver which has worked flawlessly with the program. Routes are easily created with way points and distances calculated automatically. Saved my butt when my chart plotter failed on one of my cruises. I always have it running while out on the water. Far more accurate than a chart plotter because of the detailed charts from NOAA.