ash wrote:
you'll need to state your Datum though - I use British National Grid.
I was trying to be funny with an off the cuff remark, but of course that would only work if I’d been accurate.
British National Grid is purely the format used for the positional data – the datum that I use is Ord Srvy GB because I’m using inland OS maps.
aquaplane wrote:
Does the Datum matter? I always use wotsits 84? but a Lat and Long is fixed, I thought the GPS knew the difference and converted the OS grid to a lat/long on the relevant datum.
If you using waypoints created by using the ‘mark’ button then the datum doesn’t really matter, but if you use someone else’s positional info – either read from a chart or as given above then the GPS would need to set at the correct datum.
You’re right that the GPS will happily change between OS Grid and Lat/Long. It will also change between lots of different world wide datums with varying amounts of accuracy.
I would need to change it to WGS84 to input Lady S’s figures then change it back.
I’ve just had a look at the old charts of the Clyde which I inherited with
Mistral and I see that they are also based on OSGB36 – I had it my head that old marine charts were something else.
Booby Trapper wrote:
The Garmin GPS12 does have an internal battery.
The lithium memory battery doesn't last for ever but may hold a bit of charge as long as you don't let the batteries go completely flat.
I’ve just tried removing the AA batts for 10 minutes or so, and the unit doesn’t lose the waypoints so the internal battery must have recharged to some extent.
Booby Trapper wrote:
I can't quite remember now how I got it open but I think it was just a case of prizing open the two halves with a flat bladed screwdriver. Change the battery and glue back together
That seems to be the consensus on the web – some talk that the unit might have been nitrogen filled.
Ash