# How do I use the slide rule on my Casio watch?November 25, 2008 11:59 AM   Subscribe

How do I use the slide rule bezel on my watch?

I have this Casio watch, which has an outer rotating bezel marked 10 to 95. The markings on the face read 6 to 55, KM, MPH, NAUT, and STAT. I gather it's designed to be a slide rule, but every set of instructions I can find refers to tachymeters with numbers that go much higher. Can anyone provide instructions?
posted by djb to Technology (7 answers total) 2 users marked this as a favorite

I found this page on Casio's site which explains the slide rule. (via "casio watch slide rule" google.)
posted by cowbellemoo at 12:17 PM on November 25, 2008

Yep, it's a circular slide rule. There should be a control that rotates the inner ring. Being able to rotate the outer ring to set it to match the hour or minute hand, then rotate the inner ring to set the value you're working with allows you do to time-distance calculations easily -- like "how long will it take me to go X miles at Y speed?"

Instructions

NAUT, btw, is Nautical Miles, STAT is Statue Miles.
posted by eriko at 12:19 PM on November 25, 2008

Take Two
posted by eriko at 12:20 PM on November 25, 2008

How to use a tachymeter
posted by TedW at 12:23 PM on November 25, 2008

Thanks cowbellemoo - the Casio US site was spectacularly unhelpful, I never thought to go global.
posted by djb at 12:34 PM on November 25, 2008

Yeah, I tried it to see if there were a better picture of the face but the site is repulsive and unhelpful. Anyway, I'm totally jonesin' for a slide rule right now. Thanks.
posted by cowbellemoo at 12:45 PM on November 25, 2008

A circular slide rule can be used for any multiplication or division problem. All you have to remember is that it is set up in ratios. So if you want to figure out what 10/5 is all you have to do is slide the 10 around so that it is over the 5 then go around until you find out what is over the top of the 1. There you will find, no surprise here, a 2. But wait!! What if you want to divide 1000 by 5? Just drop some zeros, do the sliding and then don't forget to add them back to your answer. So it's a good idea to do some rough mental math so that you have an idea of what the answer should be. Then you can use the watch to get the exact answer.

If you want to do a speed/time problem like how long will it take me to travel 50 miles at 25 mph simply put the speed you are traveling over the 60 (or 6 depending on your slide rule). Then find the number under the 5 (or 50) and that will be the answer in minutes. Again, apply the "reason filter" and adjust. You'll probably find a 12 in this case...but you know that you can't travel 50 miles in 12 minutes in any car so the answer must be 120 minutes.

Conversion are done the same way, you just need to know the conversion rate and then set up the ratio on the slide rule. That's it! An incredibly simple and reliable piece of equipment that requires no batteries and can be used to quickly find the answer to a great number of math problems found in daily life.
posted by tsandberg at 5:50 AM on November 28, 2008

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