On 11 Nov 2011, at 16:03, Richard Allton wrote: > The 13440 is not a 6720 doubled by a pair of singles, it is a 13440 using > only 2 singles. Do you know what the 13440 composition is then? With only 2 singles, surely they've got to be spaced 6720 changes apart to get the correct nature of rows. MF