Well John
With price you get accruacy now the RayMarine is by far the best out there it itangrades easily with navionics soft ware from your laptop and makes the mappping\GPS easier. AS to your question about the rockaccuacy it all depends on what satillite graphic data software you have the pictures and radar they take from the satelites at low tide and how much the software costs we'll depend on the accuracy of the unit. The good thing about the ray marine is that it is a good platform software and makes memory expsansion easy. There is a company in wareham called I think navonics but I know they make the plotting software for the navy and coastgaurd using airforce gps thermal, radar, and image satalites that if you get the service it updates monthly so you can transfer it to your memory card. ALso the pixle zoom speed is very fast and makes for an excelent unit. But make sure your fuses are in order because when it boots up and trys to put a fix on that satalite it draws alot of amps but thier working on that.
If YOU REALLY WANT A GOOD UNIT get the radar/map unit it intgrades between satalite and radar making it very accurate it's worth the price. Any other quetions feel free to ask.
Pete
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