andymiller wrote:[so unless you are required by the regulations to use a barometric altimeter, the eTrex 230 will do the job just as well.
GPS altitude data is often subject to quite a lot of jitter, with the result that "total climbing" numbers can be inflated by a lot - like up to 30%.
The calibration drift that you get with a barometric altimeter doesn't have nearly such a big effect.
It only really matters if you are doing DIY audax rides - calendar events and regular permanents should have an agreed figure, or at least a history of previous claims.
The trouble with non-Garmins is that without the same size of user community, things like OSM appearance, update frequency or the availability of data for non-standard areas (eg for a cycling holiday in Kerala) is at the whim of the manufacturer.
I'm sticking with my eTrex HCx until it expires. Hopefully all of the bugs in the later 20/30/dakota etx software will be fixed by then.
I've seen my eTrex 20 give occasional anomalous results - every so often the gps system seems to have an off moment and accuracy goes from the normal 2 or 3 metres to maybe 20 or so. I use my gps almost every day, all day, five months of the year and this happens maybe once or twice a month. I ride with a topographic map and the results of the gps are consistently within the stated accuracy - usually 2-3 metres. The data on the elevation display doesn't fluctuate. Occasionally if there's a weak signal, you can get a delay before the displayed elevation updates; I assume this also affects the recorded elevation - but this isn't going to impact on the total amount of climbing.
One day, I must do a climb with a known amount of altitude gain and compare that with the results from the eTrex. I wonder if anyone has ever done a head to head comparison of an eTrex 20 and an eTrex 30 on the same course at the same time.
I don't have any real experience with a barometric altimeters but I suspect you'd have to calibrate it very very carefully to get similar accuracy with a barometric altimeter (ie normally within 1 percent - although obviously this depends on the altitude where you are riding - if you are riding at low altitudes then 2 or 3 metres is going to be a greater error). I have seen the readings from a barometric altimeter (admittedly one built into a not very expensive cycle computer) quite dramatically affected as a low-pressure weather front swept in.
You do get gps noise if say you use a sight like gpsies.com and use the add/replace elevation - this does seem to introduce a lot of fluctuations if you are riding a road through steeply sloping terrain - the gps unit isn't (so far as I can tell) subject to the same problem.
I have used both the HCx and the eTrex 20 a lot. I've not experience any significant bugs with the eTrex 20 - although I've certainly had the occasional crash, as I did with the HCx. The eTrex is at least as reliable as the HCx - probably more so. Garmin to their credit have made a number of improvements to the firmware over the last couple of years (as well as bug fixes). The eTrex 10 and 30 ae significant advances over their predecessors. If you tried one I think you might appreciate the advantages.
I should of course have said 'eTrex 20 will do the job' in my original post not 230.