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pathology_docIn additional news on the slide-rule front, I found out that reading the CI scale as decimal fractions (i.e. 0.1 to 1.0 instead of the whole number actually printed), one may read the logs of these decimal fractions from the L and Ln scales simply by putting a minus sign in front. e.g. 4 on the CI scale corresponds to 0.397 on the log scale, so log 0.4 is -0.397, while ln 0.4 is about -0.92. For logs to base 10, one can of course determine logs of successive divisions of 10 by subtracting 1 from the figure given.* For natural logs, it is of course a somewhat more involved process, but the answer comes out at about -3.22. It will surprise nobody to learn that the difference between the two is 2.303 (the natural log of 10).
This avoids the horrifically messy old-fashioned way of doing things, in which one wrote the characteristic and mantissa with a bar over the former to indicate negativity, instead of a straight-out negative number. Now all you have to do (at least for powers of ten) is take the negative mantissa, drop down to CI to determine the significant figures of the decimal expansion, and divide by the appropriate power of ten.
Six inch slide rule = cute and useful, but 12" slide rule = so much more precise, and easier to read. Make mine a Pickett. *Eyes E-bay.*
* = Of course it works the other way too. Multiplying the above example by 10, we get log 4 = just over 0.6 which is one greater than -0.397, the latter of which in the old rules would have been written (bar-over-one) point six.
This avoids the horrifically messy old-fashioned way of doing things, in which one wrote the characteristic and mantissa with a bar over the former to indicate negativity, instead of a straight-out negative number. Now all you have to do (at least for powers of ten) is take the negative mantissa, drop down to CI to determine the significant figures of the decimal expansion, and divide by the appropriate power of ten.
Six inch slide rule = cute and useful, but 12" slide rule = so much more precise, and easier to read. Make mine a Pickett. *Eyes E-bay.*
* = Of course it works the other way too. Multiplying the above example by 10, we get log 4 = just over 0.6 which is one greater than -0.397, the latter of which in the old rules would have been written (bar-over-one) point six.