Thanks to Napierdeltic for your comments. I have a full screen I believe and when I open up the trackmark window in driver I see a list of Letters. Selecting a letter reveals a list of trackmarks like you said. There is no letter A,B and possibly some C's missing a the top. Which is what leads me to believe the list won,t all fit on the screen. I,ll take another look at it later when I hope to run an HST from Newcastle to York to check my work so far. My big question is to myself is "how much rolling stock and how many A1 trains I can have without the dreaded lag creeping in" I will probably have to settle for individual sessions with each session based on different area of operations. My first one is intended to give my computer a real test to see what it can handle and will be based on Kings Cross. No portals for this one, All the Stock being in the Station and Sidings in North London such as Bounds Green Depot. I am looking at 5 loco hauled, 1 HST, 2 DMU,s an hour and probably an inner surburban service. I havn,t worked out how many sets will be needed but it will be a lot! Another scenario will be less intense which will be Ferrybridge Power Station Merry-go-round services. One good thing about the ECML there are plenty of green boards and dead end lines to give me plenty of scope.