Telegraph block instrument (permissive)
Telegraph block instrument; BR. Standard modularised 2-needle (2-9)permissive (Down/Up Platform 7A/B; dynataped) 3-position type with a white black-arrowed bakelite wedge as commutator, tapper/blockbell unit underneath, and a plastic case traffolyte-plated "CHESTER No 3A". Known as a 'Penguin'.