tMapper strives for sufficient accuracy across 160 km x 180 km to guide you to within a few metres of your target. For a church spire with a two-digit x and y value, this will put you at best on the spire itself (known as a first-order point), noting that even the most precise x, y value lies within a 25 square yard rectangle. In accordance with Google Map's published precision standard, tMapper calculates to six-significant figures.
The median calculation will place you on or close to the church roof (third-order point). A small minority of conversions lie within the churchyard (fifth-order). For any discrepancy, please double-check the original trench map reference before contacting the tMapper team. The slide-show depicts 63 reference points across France / Flanders.