Ground Buzzard

Updated my Oregon 550t to version 5.00 today. So far it appears that everything is perfect: strong signals, rapid satellite acquisition, compass is right on (after re-calibration), etc. Which is not to say, of course, that bugs won't crawl out of the woodwork later... But I'm happy so far.

Problem solved; Basecamp clearly is the way to go. Thanks for the clue!

No doubt everyone else knows the answer to my problem, but the surely obvious answer eludes me. I can upload waypoints from MapSource (version 6.16.3) to my Oregon 550t (SW version 4.50), just as I've done for years with various Garmins, with no problem. HOWEVER: When I try to do the reverse, download waypoints from the 550t to MapSource, I get the message "The selected device has no waypoints on it." This is a lie, of course, since the device demonstrably has dozens of waypoints on it. (The identification of the selected device is given correctly). What am I missing (apart from adequate IQ)??? Help is thankfully appreciated.

Bolding mine. While we are still comparing GPS-predicted SR/SS times versus other predictors (NOAA, Naval Observatory, etc), and not predicted versus reality. Anyway, Janandsteve seem to be the most northerly at N53, no reported altitude, and gets up to 4 minutes per day error. I'll volunteer that I'm at N35, and right at 1000 FASL, and am consistently 2 minutes ahead of the online calculators. I would look to see where Ground Buzzard lives to make an estimate of Lat and/or elevation, but I'd guess he's closer to the equator and/or sea level. And, of course, the site's down now. Anybody else wish to add their's? All that to say, farther north=larger error? PS, and even though I'm in Kansas, our horizon isn't THAT flat, so the real SR/SS would change simply from topography. edit: fix quotey thingy FWIW, since I find myself near the center of the storm, my coordinates are 35° 08' N, 106° 31' W, elevation 5710 ft MSL.

The 450 and 550 run exactly the same firmware. This been the case, I dont understand GroundBuzzard's post and results as below, with ref to the 550t..... I cannot see it been a location thing - one of the other posters on here tried their 62s in the US ( Montana ) and they get the same discrepancies as what I do. Your tests also confirm the difference.... so I wonder why Mr Buzzard gets his bang on?.....maybe he can enlighten us? My post simply described what I did, and the results I got. I timed the sunset from my buzzardly abode yesterday. The predicted value from the 9 Garmins (see my post) was 19:52 MDT. The observed value was within a few seconds of 19:51 MDT. The apparent difference is qualitatively consistent with the fact that the point of observation, in the Rio Grande valley on the east side of Albuquerque at 5710 feet above sea level, is some hundreds of feet lower than the western horizon, roughly 20 miles away. I do not have the topographic data that would support a quantitative estimate of the time difference to be expected. The matter is further muddied by the atmospheric pressure differing from what the calculation assumes. Perhaps the question should be: How large must the discrepancy be to warrant taking it seriously?

This thread seems to have taken on a life of its own. Since I have over 40 years experience as a professional astronomer (and now am retired), I feel my qualifications might be of some value to the discussion. FIRST POINT: The entire algorithm for calculating sunset/sunrise times, in excruciating detail, can be found on Wikipedia under "Sunrise Equation". This, or another not significantly different, is the procedure the Naval Observatory uses. It is totally standard stuff. It does assume that the observer is at sea level, that his horizon is exactly 90° from the zenith (in other words, that his horizon lies in a precisely horizontal plane), and that standard meteorological conditions prevail. Any deviation from these ideal conditions will introduce a modest error in the result. Such error will increase with increasing distance from the equator, and can become quite significant at latitudes above, say, 50°. SECOND POINT: Contributions to this thread suggest that Garmin units of different ages give age-dependent differences in SR/SS times. In order to see for myself what the effect might be, I rounded up 9 different Garmin hand-held units, differing in age over a range in excess of 10 years. Specifically, these were the following, with their approximate years of manufacture: (1) eMap (1999), (2) GPS III Plus (1999), (3) GPSMAP 76S (2002), (4) Geko 301 (2005), (5) Etrex Legend HCx (2008), (6) Etrex Vista (2009), (7) GPSMAP 60CSx (2006), (8) Foretrex 401 (2010), and Oregon 550t (2010). Today, I ran each one of these at my residence, and noted what the SR/SS times were from each unit for today (3 May 2011). Every last one (NO EXCEPTIONS!) gave sunrise at 06:13 MDT and sunset at 19:52 MDT. These can be compared with the results computed from the standard algorithm (FIRST POINT, above): sunrise at 06:13:14 MDT, sunset at 19:53:18 MDT. I see no meaningful difference from the result given by all the Garmin units. THIRD POINT: In my earlier post, I suggested that Garmin might be omitting allowance for atmospheric refraction. I no longer see any justification for this suggestion, and I hereby withdraw it. FOURTH POINT: I don't see any reason to stomp on Garmin's SR/SS calculations. I don't know how to account for the discrepancies reported by others. End of diatribe!

I think Garmin simplifies the SR/SS calculation by omitting the correction for atmospheric refraction. In temperate latitudes, this has the effect of making the sunrise too late by about 3 minutes (the exact amount depends on latitude), and the sunset too early by the same amount. Atmospheric refraction always has the effect of "lifting" objects outside the atmosphere by a small amount.