Posted: Wed Jan 30, 2013 2:53 am
Wonder how long before we need to 'explain' it!:Dshaun wrote:Now that's funny! (But you've prolly gotta be older than a "Generation X'er" to appreciate it.)
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Posted: Wed Jan 30, 2013 11:26 am
How about 2 minutes???:DJPG40504 wrote:Wonder how long before we need to 'explain' it!:D
Posted: Wed Jan 30, 2013 2:09 pm
fredsheldon wrote:How about 2 minutes???:D
Slide rules are based upon logarithms.
Every number value has a unique logarithm. IIRC the 'C' and 'D' scales are base 10 logarithms.
When the logarithms of two numbers are added, the sum equals the logarithm of the product of the two numbers.
The index of the C scale is placed upon one of the numbers, the slider is placed upon the second number of the D scale and the 'result' is then read from the DS scale.
In my previous 2 x 3 = 6 example(post #5),the C index is positioned on '2' of the D scale. The slider is positioned on '3' of the C scale. The result is read as '6' on the D scale.
So adders (a slide rule is an adding device) need logs (logarithmic scales) to multiply. No neither this 'explanation' nor the scales is 'fishy'!:D
FWIW, the c/d scales may be reversed as can the two numbers and the direction of parts movement as well. Tis all 'commutative'!
