Teacher2Teacher 
Q&A #19028 
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From: Loyd <loydlin@aol.com> To: Teacher2Teacher Public Discussion Date: 2010092411:33:55 Subject: Slide Rules You can buy used slide rules on EBAY because every engineering student used to own one. I recently donated 3 or 4 slide rules to a church yard sale. So, they are still around. But make sure you get an instruction manual with it. I still have a 6 inch K&E. In college chemistry, our professor wanted us to use a circular slide rule (that was before calculators). They are the same idea as a straight rule, but you don't run off at the ends. The circular rule was very good for solving ratio and proportion which are common in chemistry and also physics. For example, 3 is to 4 as 6 is to x For the circular, place the short hand on 3 and the long hand on 4. Without changing the spacing between the hands, put the short hand on the 6. The long hand will be over the 8. But even then, slide rules are not too useful for simple arithmetic. You need to know something about logarithms, exponents and powers of 10 etc. Most circular rules were 4 inches in diameter, but I have seen them as large as 10 inches. For the straight rule, you have a slip stick and a slide, but the idea is the same but takes a bit more thinking. And of course, you still need to learn about logarithms and powers of ten, exponents etc, to become proficient. Slide rules are more for science and engineering and not for arithmetic. But they have been replaced by calculators, spreadsheets, computers, etc. Most or all computers have a scientific calculator as part of the basic software.
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