Friday, September 20, 2019

How accurate is accurate?

We live in funny times.

Never in the history of humanity has access to accurate time been so readily, cheaply and easily available to us. We take it for granted. 65% of the world’s population has at least one mobile phone.  Actually, there are 8.7 billion mobile connections on the planet compared with a population of 7.6 billion people!

Yet strangely enough, while our mobile phone delivers atomic clock time accurate down to a nano second, we are more than happy to read it at accuracy within a minute. The time displayed on the majority of mobile phones is in hour and minutes format and we are not really fussed about seconds. 10:49 on a mobile phone could mean anything from 10:49:00 at the best or 10:49:59 at the worst. For practical purpose that is close enough. But the scary part is that inaccuracy is negative – which means that if we are to catch a train departing at 10.49, we are already late.

In 1978, Seiko developed and released a railway grade quartz pocket watch with calibre ref. 7550A. This was a second generation of quartz pocket watches (with the first one being ref. 38RW cal. 3870A in development from 1976 -1978). For the next seven years, 75RW was known as the most accurate quartz pocket watch in the world. I have an example on my bench which has been running for 2 months and has been keeping time better than +1 second per week. Here is the fascinating detail in a way: This 1978 pocket watch tells the time more "accurately" than your latest phone. Why? The Seiko pocket watch allows you to read time in old fashion analogue format with a glimpse of an eye. The sweep seconds hand is always spot on to the second!

Of course I could not resist but to fire up the old Citizen quartz time tester especially designed for timing battery operated quartz watches. Like the Seiko pocket watch, this machine dates back to the same era - mid 1970's. After an hour of warm up time it was able to tell us the actual accuracy of the pocket watch. It was +0.12 seconds per day which is even less than 1 second per week! To put things into perspective, this has 3 times better accuracy than a standard modern Swiss made quartz watch and 50 times better than COSC certification of a mechanical watch.

Should you invest in one? If seconds matter, then the answer is yes.     

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