ABSTRACT
Engineers generally prefer to use circuits and systems which behave predictably. For example, when designing digital logic they tend to use circuits that perform well-defined functions like AND, OR, or NOT. A careful search through the catalogues of chip manufacturers won't uncover any PROBABLY, SOMETIMES, or WHYNOT gates! Similarly, when we buy a new watch we expect it to keep 'good time'. The hands should move or the displayed number change at regular intervals. A clock whose hands moved unpredictably faster or slower, perhaps even sometimes going backwards, wouldn't be much use - except perhaps to someone producing a railway timetable ...
