My Gaffrig (would assume same accuracy which uses garmin antennae) is about 0.5 mph off against my Lowrance.

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Both are probably pretty close, but as long as you keep using the same gps when comparing before/after it will not matter considering your speeds.

That is my plan when the rain stops, you guys are getting slammed down there as well I am pretty sure. Thanks for the info. So far you are the closest that I have heard from. Lots of people are reporting 1 to 2 MPH variance between their GPS devices. Thanks for all the input guys.

yeah, that mexican hurricane dumped an a$$ of rain here and more to come. When I bought boat up in VA, my phone app registered a max of 67.4 and the tattle tail has the same speed also, so it was spot on as well. The one thing I did notice, was my phone app has a delay of a few seconds, so if you dont hold speed for a 5-10 secs, you will see a variance also.

I don't know for sure but doesn't any GPS have a slight delay?????

Yes they do. When you ride 20 miles up a lake and back with multiple WOT runs, the recall on the Livorsi speed is what this thread is about.

I found out during prop testing because I was seeing some big discrepancies with my slip numbers. Whenever I had a co pilot they were using the numbers from the Simrad but when I was alone I just took photos of the Livorsi gps speedo. The Simrad seems to be much more accurate in all areas. In the mid range I found sometimes the Livorsi was off by as much as 4mph. The Simrad was new in 2019 the speedo in 2020. I thought it might be an update rate issue but setting at the same speed for a while confirmed they just read different at different speeds pretty much anytime over 30mph. Phone app seems to match the Simrad.