tag:blogger.com,1999:blog-266108914902271629.post332554050493517073..comments2023-09-25T08:48:48.104-07:00Comments on John Vigor's Blog: Metric nightmaresJohn Vigorhttp://www.blogger.com/profile/02215080385571534292noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-266108914902271629.post-52796199064542733992012-04-02T06:51:40.792-07:002012-04-02T06:51:40.792-07:00Anonymous- You're probably thinking of the Mar...Anonymous- You're probably thinking of the Mars Climate Orbiter. NASA uses SI (metric) for everything, but someone gave the thruster specs to the navigation computer in pound-seconds instead of newton-seconds. The computer dutifully calculated a correct course using the incorrect engine specs, which the orbiter dutifully executed- thereby flying straight into the atmosphere.<br /><br />Hubble's mirror problem was a little more involved (the root cause was a management culture issue), but the technical glitch that made the mirror warped was a scratch on the tip of a measuring rod used to check the mirror curvature. When later QA checks hinted that there might be a discrepancy, everyone thought the QA test (rather than the mirror itself) was wrong.Matt Marshhttp://www.marsh-design.comnoreply@blogger.comtag:blogger.com,1999:blog-266108914902271629.post-25735160806069019892012-04-01T04:12:56.123-07:002012-04-01T04:12:56.123-07:00Given the US is about the only country in the worl...Given the US is about the only country in the world still using the old measurements on any regular basis, the advice to find out your boat's draft in metres seems to make sense. <br /><br />By the way, rather than worrying about the speed of light in your vacuum flask, just remember there's 30.5 cm in a foot. So a yard is 91.5 cm. If your boat's draft is 5 feet, then it's 152.5 cm, or 1.525 metres. Easy. <br /><br />And it's all based on the most natural measurement of all: you have ten fingers, so everything's in multiples of ten. Much easier than all the different multiples in imperial measures. <br /><br />Wasn't the Hubble telescope a mess because someone couldn't convert feet to millimetres?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-266108914902271629.post-36780693382956552132012-03-28T15:05:34.316-07:002012-03-28T15:05:34.316-07:00SI units make perfectly intuitive sense if you use...SI units make perfectly intuitive sense if you use them on a regular basis. This is doubly so when you try to do engineering calculations.<br /><br />If you rarely use them, or if you make a point of converting to some other system before thinking "Ah, that's X far from here", it will continue to seem confusing.<br /><br />Now, if you want a bit of confusion, tell me what a gallon is. (It has three different definitions.) Or a pound. (It has at least three definitions in current use, and the same term is used for two different quantities.)<br /><br />And if you want real confusion, try converting your depth soundings to any of the systems of true natural units. We could print depth soundings as:<br />"1.24e11 YlP" (yottaplancklengths in the Planck system), "10.1 MeV^-1" (inverse megaelectronvolts in one natural system preferred by particle physicists),<br />"37 GlA" (in Hartree atomic units).<br />These are units that truly do come from the fundamentals of nature. And yes, your 5-foot keel is safe in all three cases.Matt Marshhttp://www.marsh-design.comnoreply@blogger.comtag:blogger.com,1999:blog-266108914902271629.post-48121695259748862452012-03-28T07:00:03.146-07:002012-03-28T07:00:03.146-07:00Convert your boat's draft to meters rather tha...Convert your boat's draft to meters rather than trying to convert the chart markings. Memorize it. Then you're good to go no matter how the chart is marked.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-266108914902271629.post-68140551075547388232012-03-28T01:09:42.378-07:002012-03-28T01:09:42.378-07:00Being from a metric country, I guess it all depend...Being from a metric country, I guess it all depends on what you grew up with. For me fathoms is a foreign concept. I also have a nightmare: that they would convert all the metric signs on our roads to imperial measures...<br />Stefan from BelgiumStefan Decuyperehttps://www.blogger.com/profile/05728450093085043153noreply@blogger.com