1304111 Spring motors; variable speed gearing FABRIQUES DES MONTRES ZENITH SA 15 Jan 1970 [15 Jan 1969] 1930/70 Headings F2D and F2S [Also in Division G1] In a clockwork mechanism (including a spring 9 and associated gear-wheels) for driving the recording disc 1 of a recording tachometer, one of the gear-wheels 7 is readily detachable and replaceable by another such gear-wheel. Of the two interchangeable gear-wheels, one has fewer teeth and greater diameter than "normal" for that number of teeth and the other more teeth and smaller diameter than "normal". In this connection "normal" means the appropriate diameter to make the provided number of teeth mesh exactly with the adjacent gear-wheel 8. As shown, the pair of interchangeable gears have respectively forty-eight and fifty-two teeth and their diameters are some 3% larger and smaller respectively than the diameter which would give their teeth exactly the same peripheral spacing as those of the wheel 8. The mechanism is designed for driving "daily" discs 1 through 360 degrees in 24 hours or alternatively for driving successive ones of a weekly set of seven discs through 330 degrees in successive 24 hour periods, each therefore being driven at a rate of one revolution in 26 hours. The appropriate drive rate is attained by selection of the relevant gear-wheel 7.