On a grassy elevation in Knocksentry, County Limerick, a stone of uncertain age and uncertain appearance sits close to where the Ordnance Survey once planted a trigonometrical station, the kind of fixed point used by cartographers to calculate distances and heights across the landscape. The spot height recorded there was 270 feet above ordnance datum. Whether the stone predated that practical appropriation by centuries or millennia is the sort of question the site declines to answer clearly.

The stone appears on both the 1840 Ordnance Survey six-inch map and the later 1897 twenty-five-inch revision, each time in the vicinity of the trig station, which places it within the documentary record for at least 180 years. Standing stones as a monument type are broadly prehistoric, though their precise dating is rarely straightforward; they were erected across Ireland over a very long period, sometimes as burial markers, sometimes as boundary indicators, sometimes for reasons that have not survived the intervening millennia. This particular example was identified by Celie O'Rahilly, and the record was compiled by Martin Fitzpatrick and uploaded in June 2020. The townland boundary with Knockbrack East runs roughly 90 metres to the west, which may or may not be coincidental given that standing stones were sometimes used to mark territorial limits.

Visitors should approach the site with measured expectations. A Google Earth orthoimage taken in June 2018 shows the stone as not clearly discernible from the air, and the feature may correspond either to the old trig station itself or to a low stone visible approximately 20 metres to the east of that point. On the ground, in good light, a low or partially buried stone can be easier to pick out than aerial imagery suggests, but this is emphatically a site for those comfortable with ambiguity. The elevated grassland setting means the spot is reasonably open, and the slight rise that made it useful to nineteenth-century surveyors also gives it a quiet sense of remove from the surrounding countryside.