Sentence:  Ten two-state <WSD>flip-flops</WSD> ... were formed into ten-stage ring counters representing each decimal digit in the ten-digit accumulators ... 
Meaning of the word marked with <WSD> tags:  A bistable; an electronic switching circuit that has either two stable states (switching between them in response to a trigger) or a stable and an unstable state (switching from one to the other and back again in response to a trigger), and which is thereby capable of serving as one bit of memory. (from 20th c.)