A benchmark blip!

Ha ha, I kill myself sometimes...
Spent some of the day with some local Leithers, who had been dead for possibly about 400 years. Later on I noticed this benchmark, with a strange addition.

What I think has happened is that the benchmark was carved into the pillar when the building was fairly newly built. Later, when the Ordnance Surveyors came round again, subsidence had caused the building to sink slightly, so they added the strange little hemisphere in order to raise the mark back to its original level. Fantastic attention to detail, these Victorian map-makers. They are still useful, I have measured the absolute level of many sites by tracing a chain of observations back to an old BM.