Re: Question about semaphores

Hi,

The original signal device was a ball raised or lowered on a pole. Hence the "high ball" code. Raised high, it meant that you did not have to stop.

Semaphores allowed a vertical or horizontal blade to hopefully see the signal better. The fail safe mode of a ball signal is that if no ball is raised, you must stop. A semaphore upper quadrant fails to a stop position. A lower quadrant signal fails to a "high ball" condition. The stop position in both cases is a horizontal blade.

This is one reason upper quadrants were seemingly preferred.

FWIW

Doug vV

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