What are these three engimatic stones? They could be the remains of a tomb, but I think they are all that is left of a bulky five-stone stone circle. If so then the remaining stones are the portal or entrance stones and the axial stone. The latter has a deep notch in the top, which along with its tapered sides give it a heart-shaped profile.
The alignment through this axial stone - to the south-west - also adds weight to the argument for it being a a 5-stone stone circle. The monument stands on the top of a little platform/spur and each stone is over 1m tall.
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.