“As you already well know, although such DJAMTESTERNOKHI or mechanical watches are of different what are called ‘systems’, yet they are all constructed on the same principle of ‘tension-or-pressure-of-the-unwinding-spring’. “One system of DJAMTESTERNOKHI or mechanical watch contains a spring exactly calculated and arranged so that the length of the duration of its tension from unwinding may be sufficient for twenty-four hours; another system has a spring for a week, a third for a month, and so on. BTG XXIX