Why are some quartzes more accurate than others
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Thread: Why are some quartzes more accurate than others

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  1. #1
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    Why are some quartzes more accurate than others

    Ignoring my Bulova which is very accurate, my other quartzes always vary a bit. Obviously my Casio G-shock is accurate but my Tissot loses a few seconds a month, while my Rado gains a few. Don't get me wrong - I'm happy enough with them but wonder why this is.

  2. #2
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    Re: Why are some quartzes more accurate than others

    Same reason mechanical watches aren't perfectly accurate: Physical tolerances. Tolerances on the cut of the crystal which determines its frequency. Tolerances on the electronic components that count the oscillations of the crystal. Tolerances on the gears. Quartz accuracy changes with temperature due to slight changes in electrical resistance with temperature. Many "regular" quartz movements don't have any compensation for temperature changes. They are tuned for a particular temperature and the watch will run fast or slow if temperature deviates from that. High accuracy movements include a compensation circuit that will vary the resistance in the circuit with temperature to offset accuracy drift.
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    Re: Why are some quartzes more accurate than others

    Same reason mechanical watches aren't perfectly accurate: Physical tolerances. Tolerances on the cut of the crystal which determines its frequency. Tolerances on the electronic components that count the oscillations of the crystal. Tolerances on the gears. Quartz accuracy changes with temperature due to slight changes in electrical resistance with temperature. Many "regular" quartz movements don't have any compensation for temperature changes. They are tuned for a particular temperature and the watch will run fast or slow if temperature deviates from that. High accuracy movements include a compensation circuit that will vary the resistance in the circuit with temperature to offset accuracy drift.
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  5. #4
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    Re: Why are some quartzes more accurate than others

    Quote Originally Posted by MX793 View Post
    Same reason mechanical watches aren't perfectly accurate: Physical tolerances. Tolerances on the cut of the crystal which determines its frequency. Tolerances on the electronic components that count the oscillations of the crystal. Tolerances on the gears. Quartz accuracy changes with temperature due to slight changes in electrical resistance with temperature. Many "regular" quartz movements don't have any compensation for temperature changes. They are tuned for a particular temperature and the watch will run fast or slow if temperature deviates from that. High accuracy movements include a compensation circuit that will vary the resistance in the circuit with temperature to offset accuracy drift.

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    Re: Why are some quartzes more accurate than others

    I would add that a lot of the variation is down to production decisions. The majority of quartz watches are rated to 15, 20 or even 30 seconds per month. Sometimes you will pick up a nominally 30 SPM watch and be lucky enough to discover that it averages about 1 or 2 SPM. The next chap who comes along and buys the same model from the same shop may find it performs a lot nearer to its 30 SPM limit. Whilst it is true that temperature bears the greatest responsibility for any given quartz watch's daily rate variance, between individual watches the difference in rates is more often down to production tolerances.

    In the majority of quartz watches, the (usually) XY cut crystal oscillators are very cheaply mass-produced. This is true even for quite expensive watches and what it means is that the brand simply cannot guarantee the rate of the movement to much better than a second per day. Besides thermocompensation, there are other ways to improve accuracy, including using a high power, higher frequency AT cut crystal, or by using a VFA approach (carefully selecting a good quality crystal and then fine-tuning the rate to best fit its thermal properties). Or, of course, Bulova's method using an unusually shaped oscillator to combine flexural and torsional resonance modes in a high frequency XO for reduced thermal sensitivity.

    And we have to remember that there aren't all that many people who care about super accuracy in their quartz watches. Most cheap quartz watches are already immeasurably more accurate than mechanical watches and if you ever did want the precise time you would just look at your phone anyway. Or have an RC / GPS watch. So there just isn't enough demand in the market for most manufacturers to bother trying to achieve more consistent rates in their quartz watches.
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    Re: Why are some quartzes more accurate than others

    well ... I was going to say that not all quartz movement are created equal ... but this is a much better answer

    Quote Originally Posted by MX793 View Post
    Same reason mechanical watches aren't perfectly accurate: Physical tolerances. Tolerances on the cut of the crystal which determines its frequency. Tolerances on the electronic components that count the oscillations of the crystal. Tolerances on the gears. Quartz accuracy changes with temperature due to slight changes in electrical resistance with temperature. Many "regular" quartz movements don't have any compensation for temperature changes. They are tuned for a particular temperature and the watch will run fast or slow if temperature deviates from that. High accuracy movements include a compensation circuit that will vary the resistance in the circuit with temperature to offset accuracy drift.

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