The block instrument consists of a small cabinet; its front face displays two indicators telegraph needles and has a commutator handle ( some early designs of block instruments had miniature semaphore arms instead of needles ).
12.
In effect, this mechanism is very similar to the colour light signal that is included in an electrically operated semaphore signal, except that the omission of the semaphore arm allows the roundels to be miniaturized and enclosed in a weatherproof housing.
13.
Thanks to its construction, the Bavarian distant signal could also be fitted to the mast of a home semaphore signal, so that, for example, the combination of'proceed slowly'and'expect clear or proceed slowly'( Hp 2, Vr 102 ) could be displayed on the same mast using three semaphore arms.
14.
For most types of semaphore arm, the colour of light shown when the arm is in the " on " ( most restrictive ) position generally corresponds to the colour of the arm itself ( i . e . red for a stop signal, yellow for a distant signal ).
