Old B&M charts: what aspects do the signals represent?

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Old B&M charts: what aspects do the signals represent?

Postby BostonUrbEx » Mon Sep 04, 2017 10:39 am

Here is a sample of a stereotypical B&M chart: http://www.nmro.org/samp-n-plan.jpg

I'm looking for a key for the signal masts, as the different patterns represent the different potential signals that can possibly be displayed.

The only thing I can figure out for certain is that the circles with a horizontal line through them are only capable of displaying red. The rest have seemingly endless possibilities.

EDIT: also, circles with a diagonal line from top left to bottom right are heads that can only display a red or yellow.
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