Gps
How a GPS functions has to do with five main items and are not listed in order of importance. The first is knowledge. You need to know how to work with your GPS and to understand datum (UTM, Decimal Degrees, etc.).
Secondly, the quality of the signal the GPS is receiving while you are working in the field or on the trail. Most models post or display a DOP, or PDOP number. Simply stated, it is the quality of signal the unit is receiving for the highest degree of accuracy at the time you are gathering waypoints or tracks. The lower the PDOP or DOP number, the higher degree of accuracy the unit is receiving. This will vary from hour to hour during the day.
Third, has to do with multipathing. This is where your GPS is receiving the signal and is also receiving another signal that is bouncing off the glass of a building, or the windshield of your 4X4.
Fourth, your unit should be WAAS capable (Wide Area Augmentation System). This will improve the accuracy of your unit. If your unit is not WAAS capable, older units can provide a function called waypoint averaging. This takes longer but in most cases we don't need that kind of accuracy.
Fifth, the kind/material of the antenna. Some antennas like the helix antenna pick up and maintain the GPS signal better than other antennas.
Here is my bias. I prefer either a Garmin and Trimble GPS. Most units come with software, but there is other software you can download. An example is DNRGarmin that works great and is free. EasyGPS and other free software works great if you are working with limited waypoints and tracks. They offer a version that will handle additional waypoints and tracks but at a cost. DNRGarmin doesn't have a limit and is still free.
Ok, that's my simple thoughts.
Don