This is only a 'possible'. I noticed the stone set into the bank along the trackway as I was walking to Toor (County Wicklow) stone circle. The stone has a line of long cupmarks running across it. Some people consider them to be quarryman's marks, but I believe that they are decorative. They can also be found at other Wicklow/Dublin sites such as The Piper's Stones (County Wicklow), Castleruddery Lower (County Wicklow), Ballyedmonduff (County Dublin) and Glassamucky Mountain (County Dublin).
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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.