Woops,I'm sure that someone had this figured out already but The 8 inch wide X 4 inch deep drill hole is 2 cordell = 380 feet plus the shoulder 1/2 way down = 1 cordell + 2 cordell = 3 cordell or 570 feet, sorry about that, flat bottom drill hole indicates top and bottom are the same and they are different than the cone shape ones, as are the angled ones with a long tapered side kinda like a transminion funnel, even if there is one small ( 1/4 inch ) it means the same as the larger if its on an angle, it will be on another rock with another mark, find the other one, it should be 90 feet ( viking long boat length, there are different boat lengths other than 90 feet ) and look at it as if you are driving tent stakes and securing the top of a tent, just another triangle with ropes. Good grief I hope this makes sense