Second Series/Pathfinder
Blackadder will be adding content over time
Published by the Ordnance Survey from 1965 onwards the Second Series, later to become Pathfinder, maps were the replacement of the Provisional/First Edition 1:25,000 scale.
Sheets are predominately 2 x 10km squares (horizontally) though some sheets at coastline areas are of variable sizes.
Sheets will start to become out of copyright at the beginning of 2016.