Recent Changes for "Using a slide rule" - Obsolete Skills Wiki

Using a slide rule

JabberWokky — 2008-03-10 21:00:56

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	+ + * My wife informs me that among her undergraduate students, recognizing a mathematical answer is blatantly off is nearly never caught; there is very little common sense reckoning done to double check an answer.

Using a slide rule

2008-03-10 19:15:00

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- ''2008-03-10 19:12:25'' [[nbsp]] Well, my point would be that even many people who are fully aware of what logs are didn't necessarily think about them when using the slipstick to obtain an answer, particularly if they used them all the time. They just wanted to know what, say, 67.4 * 3.62 was for whatever reason. Knowing the general magnitude of the answer so that when they read "244" off the scale it meant 244, not 24.4 or 2440 was required of course, but there are many mental approaches to that, rather than actually thinking about adding exponents together. Personally, I'd mentally round the 67.4 to 70 and the 3.7 to 4, and know my answer was something in the rough vicinity of 280 - a bit less, since I rounded both up. I suspect there was a class of people that used slide rules on a daily basis who had forgotten what they had ever learned about logarithms. In many cases, their mental process of placing the decimal point in the answer was probably based on visualization of the physical problem they were solving.	+ ''2008-03-10 19:12:25'' [[nbsp]] Well, my point would be that even many people who are fully aware of what logs are didn't necessarily think about them when using the slipstick to obtain an answer, particularly if they used them all the time. They just wanted to know what, say, 67.4 * 3.62 was for whatever reason. Knowing the general magnitude of the answer so that when they read "244" off the scale it meant 244, not 24.4 or 2440 was required of course, but there are many mental approaches to that, rather than actually thinking about adding exponents together. Personally, I'd mentally round the 67.4 to 70 and the 3.62 to 4, and know my answer was something in the rough vicinity of 280 - a bit less, since I rounded both up. I suspect there was a class of people that used slide rules on a daily basis who had forgotten what they had ever learned about logarithms. In many cases, their mental process of placing the decimal point in the answer was probably based on visualization of the physical problem they were solving.

Using a slide rule

2008-03-10 19:12:25

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	+ ------ + ''2008-03-10 19:12:25'' [[nbsp]] Well, my point would be that even many people who are fully aware of what logs are didn't necessarily think about them when using the slipstick to obtain an answer, particularly if they used them all the time. They just wanted to know what, say, 67.4 * 3.62 was for whatever reason. Knowing the general magnitude of the answer so that when they read "244" off the scale it meant 244, not 24.4 or 2440 was required of course, but there are many mental approaches to that, rather than actually thinking about adding exponents together. Personally, I'd mentally round the 67.4 to 70 and the 3.7 to 4, and know my answer was something in the rough vicinity of 280 - a bit less, since I rounded both up. I suspect there was a class of people that used slide rules on a daily basis who had forgotten what they had ever learned about logarithms. In many cases, their mental process of placing the decimal point in the answer was probably based on visualization of the physical problem they were solving. + + Ability to estimate answers is something sadly lacking these days, of course. --209.204.181.86

Using a slide rule

2008-03-10 07:58:21

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	+ ------ + ''2008-03-10 07:58:21'' [[nbsp]] I would think sliding and lining up etc with no knowledge of logs is playing rather than using: a trap with using slide rules was to remember that you needed to add the exponents from each of the numbers being multiplied in order to find the answer (or subtract them when dividing) --221.133.214.214

Using a slide rule

2008-03-09 21:18:43

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- === Other scales === - You will note in the pictures that there are more scales than just the two adjacent log scales needed to perform multiplication. Most slide rules had scales for trig functions, scales for taking square roots, reverse scales for taking reciprocals, etc. The wiki article discusses some of the other scales which might commonly appear on a slide rule: http://en.wikipedia.org/wiki/Slide_rule#Other_operations -
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	+ + === Other scales === + You will note in the pictures that there are more scales than just the two adjacent log scales needed to perform multiplication. Most slide rules had scales for trig functions, scales for taking square roots, reverse scales for taking reciprocals, etc. The wiki article discusses some of the other scales which might commonly appear on a slide rule: http://en.wikipedia.org/wiki/Slide_rule#Other_operations

Using a slide rule

2008-03-09 21:16:37

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	+ === Other scales === + You will note in the pictures that there are more scales than just the two adjacent log scales needed to perform multiplication. Most slide rules had scales for trig functions, scales for taking square roots, reverse scales for taking reciprocals, etc. The wiki article discusses some of the other scales which might commonly appear on a slide rule: http://en.wikipedia.org/wiki/Slide_rule#Other_operations +

Using a slide rule

JabberWokky — 2008-03-09 21:08:56

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	+ * So fix the entry!

Using a slide rule

2008-03-09 21:06:55

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	+ ------ + ''2008-03-09 21:06:55'' [[nbsp]] Concerning "knowledge assumed" - logarithmic scales are what make the thing work, but you don't really have to know anything about logarithms to use the device. Adding the logarithms together is done physically by lining up the scales and crosshair on the two numbers you want to multiply. You don't have to be aware of why it works when you're using it. --209.204.181.86

Using a slide rule

JabberWokky — 2008-03-09 19:13:03

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- Slide rules came in both linear and circular versions, the latter allow one to become completely dizzy in doing long multiplications!	+ Slide rules came in linear, cylindrical and circular versions, the latter allow one to become completely dizzy in doing long multiplications! Cylindrical sliderules were amazingly expensive and precise. The late Dr. Issac Asimov, famed for his science and science fiction writings, owned a five foot cylindrical sliderule which he kept in the corner of his office.

Using a slide rule

2008-03-08 08:06:52

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- \|\| When did this skill become obsolete? \|\|	+ \|\| early '70s \|\|
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- \|\| What does the reader need to know to use this guide? \|\|	+ \|\| Logarithms in mathematics \|\|
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- \|\| When is this skill still useful? \|\|	+ \|\| Understanding log scale graphs \|\|
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- Slide rules use the concept of logarithms to allow complex calculations to be done by simply comparing two rulers.	+ Slide rules use the concept of logarithms to allow complex calculations to be done by simply adding linear quantities on adjacent but independently moved logarithmic scales.
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- The basic theory here is you use the properties of logarithms to change multiplication into addition. log x + log y = log x*y. You move the slide tothe logarithm of the first number, and then add the length of log of the second number. You then read off their combined length in logarithm space, which effectively multiplies the numbers.	+ The basic theory here is you use the properties of logarithms to change multiplication into addition. log x + log y = log x*y. You move the slide to the logarithm of the first number, and then add the length of log of the second number. You then read off their combined length in logarithm space, which effectively multiplies the numbers. + + Slide rules came in both linear and circular versions, the latter allow one to become completely dizzy in doing long multiplications!

Using a slide rule

JabberWokky — 2008-02-27 11:36:44

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- [[Include(Seed)]]	+ =====

Using a slide rule

BrentLaabs — 2008-02-27 05:58:38

i know a little about slide rules, but there are more indices i don't know well

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- \|\| Which field does this skill apply to? \|\|	+ \|\| Mathematics, Engineering, Sciences\|\|
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- \|\| What made this skill obsolete? \|\|	+ \|\| Advent of electronic calculators \|\|
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- Then, describe the skill! Tell us how to perform the task. Photos really help!
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	+ + Slide rules use the concept of logarithms to allow complex calculations to be done by simply comparing two rulers. + + === Multiplication === + To multiply two numbers, get the values in scientific notation, i.e. ''a'' * 10^''b''^. Take the abcissa ''a'' from the first number. Slide the center part so that the number "1" (referred to as the index) on the {{{C}}} scale to the number ''a'' on the {{{D}}} scale. Then find the the abcissa of the second number on the {{{C}}} scale. See what's right below it on the {{{D}}} scale -- this should be your answer. + + You still need to handle the exponent part, but that's simple: 10^3^ * 10^2^ = 10^3+2^ = 10^5^. Used correctly, you can get about three significant figures out of your use of the slide rule. + + The basic theory here is you use the properties of logarithms to change multiplication into addition. log x + log y = log x*y. You move the slide tothe logarithm of the first number, and then add the length of log of the second number. You then read off their combined length in logarithm space, which effectively multiplies the numbers.

Using a slide rule

JasonAller — 2008-02-17 20:16:56

Upload of image Sliderule_Close.JPG.

Using a slide rule

JasonAller — 2008-02-17 20:16:23

Upload of image Sliderule.JPG.

Using a slide rule

JasonAller — 2008-02-17 20:16:06

seeded page to upload photos

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	+ [[Image(Sliderule_Close.JPG, right, thumbnail, 400, "Close up of sliderule")]] + + \|\|<bgcolor='#E0E0FF'>'''Field'''\|\| + \|\| Which field does this skill apply to? \|\| + \|\|<bgcolor='#E0E0FF'>'''Went Obsolete'''\|\| + \|\| When did this skill become obsolete? \|\| + \|\|<bgcolor='#E0E0FF'>'''Made Obsolete By'''\|\| + \|\| What made this skill obsolete? \|\| + \|\|<bgcolor='#E0E0FF'>'''Knowledge Assumed'''\|\| + \|\| What does the reader need to know to use this guide? \|\| + \|\|<bgcolor='#E0E0FF'>'''When useful'''\|\| + \|\| When is this skill still useful? \|\| + + Then, describe the skill! Tell us how to perform the task. Photos really help! + + [[Include(Seed)]] + + == Photos == + + [[Image(Sliderule.JPG, thumbnail, 400, "Overall view of a sliderule")]] + + == Other references == + + * list other references about this skill here + + [[Comments]]