Grid Reference
Standard two-letter and six-figure map (100m) reference using the National Grid in Great Britain and the Irish Grid in Northern Ireland. The Irish Grid has only one prefix letter but it is common practice to precede it with the letter I to make identification clear.
Station Level
The level of the station is, generally, the altitude taken from the banks of the gauging station in metres above Ordnance Datum or, in Northern Ireland, Malin Head.
