In Saint Cleeres parish in Cornwall, there are upon a plain six or eight Stones, such as are upon Salisbury plain, which like them two will be mistaken in the telling; so that when they are told over again, they will be found over or under the first number. A thing, that happens (no doubt) meerly by their confused standing.
From ‘Britania Baconica: or, The natural rarities of England, Scotland, and Wales’, written by J Childrey (1662).
I assume this is the right location, it doesn’t seem unreasonable?