The national constituency voting compositions, 1955-1987 (Colour).

705 consistent parliamentary constituencies (Appendix C) projected upon eleven electoral triangles, with two party contests drawn as a histogram and Northern Irish dissensions as a line to the right of the triangles — software by author on an Archimedes computer

These frames are taken from an animation which clearly shows (unlike this image) that it was often not the same seats which fielded only two candidates in the early years. The change from predominantly two party politics, to three, is clearly illustrated, as is the way today’s sickle took shape early on. The jumps up to the Liberals in February 1974 and 1983 can also be seen, as can the growing awareness of tactical voting, resulting in relatively few seats being near the centre of the triangle. The seats are coloured by the winning party, and some of the best results for the Conservatives in 1987, in terms of three party politics, can be seen to have actually been losses to the (green) nationalists.