Gear

GPS accuracy depends on many things. I think the main ones are:

1) Number of satellites - you need 3 for a 2D fix and >=4 for a 3D fix. I doubt if a fix based on 2 satellites is worth much because global positioning is basically glorified trigonometry.

2) Satellite geometry, ie. where in the sky the satellites are. You need a good "spread" of satellites to get better accuracy.

3) Interference from the ionosphere. I believe the satellites "broadcast" corrections based on known ionospheric conditions. The GPS receiver uses these corrections to work out how far away the satellite really is, based on the length of time it took for the signal to get from the satellite to the receiver. Apparently, GPS accuracy is better at night because the atmosphere interferes less with the signal.

fine accuracy is good if you've got a bomb to drop but for us mere mortals, finding just where we are on the map (approximately) can be most useful. mine occasionally has a fit and says 3m so coupled with the map's 7m accuracy (or something like that) i'll be somewhere around there. if you forget your map it will tell you exactly where you're lost (not a day i wish to repeat) but it will backtrack you.
also useful for finding car at NEC or airports, when drunk and can't remember where you left the hotel.
the yellow one's batteries can rattle around inside and switch the unit off, so if you are using it to track where you've been, check that it's still switched on occasionally.
all in all its accuracy is more than good enough and is probably better than most people's map reading.

Oh bum!
I really thought somebody was going to tell us how to put in a map ref. because poor stupid me cannot see how to get more than 3+3 figures off the map?

Yep, a GPS is useless if your basic navigation skills aren't up to scratch. As far as walking etc. is concerned, a GPS should be used as a secondary navigation tool, not a primary one, such as a map and compass. As Parky says, a GPS is next to useless without a decent map. Also, remember that a GPS can only navigate "as the crow flies" between waypoints, which isn't a lot of use on a horseshoe ridge in fog. For this reason also, back track logs should only be used as a reference - they won't navigate you back exactly the way you came (Garmins are generally worse than Magellans in this respect).

Bryan, a six figure map reference is usually enough. Just enter the other 2+2 digits as 0 or something. Given the map accuracy and GPS (estimated!) accuracy, you're going to be a few metres out anyway.

Can I ask a question from all you ETrex-owning people?

Is there an easy, quick way of saving the current position in the eTrex?

I ask 'cause I need to get a GPS for boating purposes - only needs basic functions, location mainly.

But it is kind of essential to be able to instantly save the current position if someone goes overboard. Dedicated Marine GPS's usually have a 'MOB' button for this - but a friend reckoned you could do the same in the eTrex by holding down a button.

The accuracy thing - the GPS system can denote a point in space about the size of a rugby ball on its end. It takes about three hours to do and kit the size of a tea chest. Triangulation survey - great work if you can get it.

To speed up entering waypoints, one can skid sideways over the existing grid reference using the down button, but if you overshoot (or, I think, try to go backwards)this can chuck you out of the page. Just set the last two figures on each line to 50 to centre the 100 metre circle of error, ie,EEE50 NNN50.

In France I have the problem of changing the datum from WGS84 to EDM50 to use the 50thou maps in the GR guidebooks. Why IGN decided to use WGS84 for the new 'GPS ready' 25 thou series maps, I don't know.

Alastair,
with a etrex, you press and hold enter for about 2 seconds to mark a waypoint (instructions p15). The screen changes offering you the next available waypoint number and you press enter again to accept this.

Accuracy - WAAS/EGNOS corrections normally settle down to around 1 metre ETE after about 15 minutes (with a clearish view of the sky) in most of the current GPS receivers. Most GPS receivers can also average (this is on by default in most Magellan receivers) when you're standing still, so a reasonably steady fix can be achieved after a little while. With GPS receivers that don't/can't average, you'll notice that your position will wander, sometimes by several metres, when you're standing still.

I used to have a etrex :(

If I hear of anyone flogging a dubious English language eTrex and other quality kit on my side of the Ditch, I'll let you know, Guy.

WAAS is US only, EGNOS is alleged to be going operational in April 2004. Anybody any idea how to make it work with an eTrex? Or is it 'automatic'?

I don't think WAAS/EGNOS is supported on the basic eTrex, although it is on the Venture up. I think it's off by default on all but the newer Garmins and can be switched on via the System menu (this is all from memory, BTW!).

Apparently, Magellan do it the other way round, ie. you get WAAS by default and you can't switch it off (well, you can if you know the unsupported sequence of key presses). This causes problems for people in areas not supported by WAAS corrections but which can pick up WAAS signals from a satellite, such as in Australia. In this case, the corrections can make GPS accuracy much worse than it would be without WAAS.

As I have at last manage to buy French 50K mapping (www.ign.fr), standard accuracy is good enough for me. Edition 3 is WGS84 too. I guess it's only the maps in the Grande Randonnee guidebooks that are still on the European 1950 datum.

Hi folks . I'm new to this so bear with me.
1.
I to have the basic eTrex. I wouldn't be without it on the hill. I dont use it to its full capacity like typing in routes etc. I relly can't be bothered BUT all is about to change (I hope). I have purchased the SMC GPS Data Sets disc and have the GPSU downloaded. I have the PC cable. Now can anybody tell me how to upload from this setup. I'm not sure but I don't think the wee yellow box supports PCX5.
2.
I am seriously thinking of selling my eTrex and getting a GEKO 301. Does anyone out there have a 301 and would you recommend it.

I have the Geko 301 Mike and yes, I would recommend it.
It's tiny, very lightweight and the smaller (than Etrex) screen size is something you soon get used to, so much so that when I now hold an Etrex it seems huge!
The top-mounted buttons are particularly useful if, like me, you intend fitting it to the handlebars of a bike.

anybody want to buy an e-Trex?
Excellent condition.
Latest software version 2.14
£50. Buyer pays postage