This page lets you track the possible locations of Mr. X in the Scotland Yard board game. This is based on the Ravensburger 1983 board (where point 128 is a tube station), there seem to be different versions around.
It works by entering the known location of Mr.X and the tickets used by him from there on. Changing the start position resets the ticket list. Possible location on every intermediate turn are shown from left to right. Branches can stop on every intermediate turn, if this location is not reachable by the used ticket type. On the very right the possible locations are shown, duplicates are possible, if a location can be reached via multiple paths.