... have had to post a screen shot as Excel files are not accepted as a valid file type, so you may need to go to the gallery to read the original text. Hope this works. Tony. 2151_201728_420000000.png The formula I use provides the same result as you quote for end throw but mid throw will not necessarily be the same value, plus you also need to add a passing clearance measurement to provide your track centers. Attached tables illustrate results for EM from using basic trig formula calculated out by Excel. Attachment: attach_1363_1835_Track_Centres.jpg 476 posted: 20 Feb 2012 23:10 from: Martin Wynne Hi Derek, Ian, Mike, Tony, Thanks for your feedback. But as I mentioned, the geometry on circular curves is not the difficult part. The difficult bits are a. doing the maths for transition curves, slewing zones, and the turnout roads through double junctions; b. deciding on an acceptable allowance for model discrepancies such as end-play in axle-boxes, off-centre bogies, body-sway, etc., ...