Foel Dduarth Arrow Stone

Just a couple hundred yards from Hafod Gelyn cairns is this Arrow stone, there are quite a few round here and this is a good example. Eric, the dogs and I entered the area where I knew it would be, I said to the lad look for a quite a big stone with lines carved onto it. Five seconds later “is this it ?”
It most certainly was, no time wasting here.

When Idwal came here he mustn’t have had his glasses on because he saw the letters RRP carved amid the lines, but there is more, it isn’t just initials but a whole name R R PENLAND. How rude.

Just what are they though ? Arrow stones ? presumably so called because the stone was used to sharpen arrow heads. But really ?
I haven’t heard a single explanation that sits well, are they even properly ancient, who knows, not me, or anyone it seems. Geeeooorge !!!