I need to get a GPS that can navigate me to the front door of my destination...What is the most accurate out there? My friend has an old Alpine in his car and it is several hundred yards off at times. It can be either hand held or a CD/ reciever unit for my car...Thanks

I have a Garmin 180 and it is very easy to use. I run the channels at nite and use it to help me spot the unlighted bouys. Always seems right on.

Speaking of GPS, does anyone know how accurate the older Garmin Gps are, especially for speed readings?

Do they still use differential GPS? That is what I have for my boat. It looks at a known location and measures the error and then calculates your exact position. Very cool. Is this WAAS thing similiar?

Jon

Kindof, Jon. DGPS uses a land-based differential beacon. Beacon knows exactly where it is, it receives the fix from GPS and sends out a corrective fix. WAAS does something similar, but via a satellite in the sky. Hence the name Wide Area Augmentation System. Important for offshore racers: WAAS can also do 3D .. it will plot your in-flight-trajectory.

I get a GPS trade magazine. They did a comprehensive test.

DGPS and WAAS offer similar accuracy on the whole. Particular units will lean towards the good or bad end of their range, but the units are both very accurate. WAAS is indeed the better bargain. If you already have DGPS and are in a serviced area, then there is no reason at all to consider replacing with WAAS unless a newer unit offers a feature you require. Both technologies are significantly more accurate than "normal" GPS. Even "normal" GPS is better than it used to be due to SA being discontinued (which was a random scrambling signal).

Update time is a factor in giving good position and speed info. Some, but not all, older units used slower update times. Most, but not all, newer units have faster update times.

Even slow update units will give an accurate speed reading if you are traveling at a steady speed and give the unit time to update.