Several weeks ago I sat on the wall in front of this stone scratching my head and wondering where it could be. To be fair I wasn't looking for something this big, nor was I expecting the stone to be earthfast. I was looking for a little rock with a bit of rock art on it, perhaps set into a wall. It is quite easy to find when you know where it is - behind the mailbox to Bracken House.
The panel is 1.5m x 1m and has 16 cup-marks spread across it. There doesn't seem to be a pattern to them.
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This is an explanation of (and a bit of a disclaimer for) the coordinates I provide.
Where a GPS figure is given this is the master for all other coordinates. According to my Garmin these are quite accurate.
Where there is no GPS figure the 6 figure grid reference is master for the others. This may not be very accurate as it could have come from the OS maps and could have been read by eye. Consequently, all other cordinates are going to have inaccuracies.
The calculation of Longitude and Latitude uses an algorithm that is not 100% accurate. The long/lat figures are used as a basis for calculating the UTM & ITM coordinates. Consequently, UTM & ITM coordinates are slightly out.
UTM is a global coordinate system - Universal Transverse Mercator - that is at the core of the GPS system.
ITM is the new coordinate system - Irish Transverse Mercator - that is more accurate and more GPS friendly than the Irish Grid Reference system. This will be used on the next generation of Irish OS maps.