SimSig goes Doon-the-watter to the Clyde ports of Gourock, Wemyss Bay, Largs and Ardrossan and on down the Ayreshire coast to the town of Ayr. The Sim represents the 1980s, 3 panel, NX box located at Paisley Gilmour Street (as it was in 2008). This has since (Christmas 2011) been absorbed into the new West of Scotland Signalling Centre located at Cowlairs.
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Read about it in the manual, download it from the Downloads area, and purchase a license from the shop.