Path: csiph.com!aioe.org!.POSTED!not-for-mail From: Martin Brown <|||newspam|||@nezumi.demon.co.uk> Newsgroups: sci.electronics.design Subject: Re: OT: Current standard for watch precision Date: Tue, 7 Feb 2017 09:58:31 +0000 Organization: Aioe.org NNTP Server Lines: 50 Message-ID: References: NNTP-Posting-Host: 3GhpzT84sg/pRzW4FgEbGg.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 X-Notice: Filtered by postfilter v. 0.8.2 Xref: csiph.com sci.electronics.design:446630 On 06/02/2017 11:45, Pimpom wrote: > On 2/6/2017 11:43 AM, Phil Allison wrote: >> Pimpom wrote: >>> >>> >>> What would be considered a "good" wristwatch today in terms of >>> timekeeping precision? Forget about build quality, price, shock- >>> and waterproofing, etc. >>> >>> Half a century ago, a wristwatch with a-minute-a-month accuracy >>> might have been labelled a chronometer. What standard would you >>> apply now? >>> >> >> ** The Quartz standard, of course. >> >> Goolge has heaps of info on this topic: >> >> http://www.chronocentric.com/watches/accuracy.shtml >> > Perhaps I should rephrase the question. I meant to ask what level of > accuracy would be considered good for a consumer wristwatch nowadays. Its possible to get stuff as bad as 15s/day untrimmed if they don't get the load capacitor network round the crystal right. Older Meade LX200 telescopes suffer from this fault on their realtime clock :( They solved it by adding a GPS function so it resets the clock on newer ones! > For example, I bought a Chinese analog-digital wristwatch from > www.aliexpress.com last month and have been monitoring its accuracy. I > do this by comparing it to a freshly synced computer clock. It's now > exactly one month since I synced it to the computer clock. The analog > section is ahead by 6 seconds and the digital one is behind by 35 secs. > The errors may not be linearly cumulative but I think it's pretty good > for a US$7 watch. It depends on the cut of the crystal and whether or not it is being thermally stabilised by being worn on the wrist for some of the time. (or worn outside in extreme conditions) It isn't hard to get a couple of seconds a month or better with a simple temperature compensation scheme. I made a direct drive LCD chronometer which keeps time free running very nicely 2s/month after being trimmed against MSF Rugby for a couple of days. Not fully temperature compensated or it would be even better. Its actually used as a sidereal clock by flicking a switch after it has been calibrated. -- Regards, Martin Brown