The Retriangulation of Northern Ireland.
After OSNI was set up in 1921, OSGB retained responsibility for the geodetic triangulation. The second World War delayed the re-triangulation of Great Britain, but when it was completet, resources were made available to OSNI and observations on the re-triangulation began in the spring of 1952.
The network consisted of nine stations plus three in the Repiblic of Ireland and a number of cross-channel connections to GB. The adjustment accepted the position of three of the original Principal Triangulation points in order to scale and orientate the new triangulation. These points were Divis, Knocklayd and Trostan. Comparisons to the (then) recent re-triangulation of GB showed only a slight discrepancy between the two re-triangulations.