I AM pleased that Jeff Nisbet has managed to do what I have tried in vain to do for the past two years which is to get media interest into what may well be the first examples of art in Scotland ("New theory sheds light on mysterious stone balls found across Scotland", The Herald, May 4) with the suggestion that the balls are, perhaps, apprenticeship pieces for entry into the profession of stone masonry.

I have measured more than 360 of these balls and even had a sculptor friend carve two imitation ones and found that the target diameter was always 69mm (slightly less than a tennis ball). This is important as I also have spent the last two years measuring more than 360 neolithic cup and ring marks and found the target gap between rings across five countries – including La Palma in the Canaries, and Carschenna in the Swiss Alps – to be 23mm plus or minus 2mm. This is, I suggest, the basic unit of the Neolithic measuring system and so I call it the Neolithic inch;12 of which is the Neolithic foot and 36 of which makes a Neolithic yard or pace.This thus may prove to be the basis of the imperial measurement system.

Further research shows that a container 4x4x3 neolithic inches holds a pint of liquid or a pound of barley up to the present day. The Neolithic inch is the average width of a squashed adult male thumb or the length of the final section of the little finger. Hence our bodies carried an objective ruler that couldn't be lost and supports Protagoras when he declared that "man is the measure of all things". There is much more to be said, but I conclude with a further curiosity and no doubt a mere coincidence that the "Neolithic inch" of 23 mm is the same as the diameter of the latest £1 coin.

Tim Flinn,

Beech Cottage, Garvald, East Lothian.