This is a book specifically created to enable hand-computations of most of the functions of a modern scientific calculator to six decimal places.

At the time it was written (1891), there were no calculators that people could readily use, and this situation did not change appreciably until 1960's. The book gives base 10 logarithms of numbers from 1 to 10000, and logarithms of trigonometric functions (sines, cosines, tangents and cotangents) as well as the natural values of trigonometric functions (sines, cosines, tangents and cotangents) to six decimal places, enabling one to perform complex, "floating point" multiplications and divisions as well as trigonometric computations, by only using additions and subtractions, most of the time.

Should one have a "four-function calculator" with a memory (add, subtract, multiply, divide, and M+, M-, etc.) which costs only few dollars, this little book turns it into a calculator with scientific functions while teaching one how to perform complex calculations by hand (when one is out of batteries, for example). At the present time, most people exclusively rely on electronic calculators or software programs that run on hand-held devices to perform any computations they need without really knowing how these ever work, or how to check correctness of the answers they get. This book supplies one of the ways to accomplish this.

Whenever you have time, you might consider reading a story by Isaac Asimov, titled "The Feeling Of Power".
It was first published in 1958. The story takes place in an age when everything is run by computing machines, controlled by human beings, just like today. However, no one knows how they work exactly, and only machines design the new machines. They just use the machines' output in various formats, and they do not know how to perform even simple arithmetic calculations, like addition, and this does not bother them as most people are not even aware of the "lack of a problem".

Some repair technician, working on scrap computer electronics for a hobby, figures out how the machines actually add two numbers, and develops a technique for himself to perform addition on a piece of "paper" by hand. He becomes happy for a while, but then he makes a mistake and tells his superiors what he has accomplished. He becomes instantly famous and a "national security problem" due to his knowledge...

The story is like an "immunization" for "acute and incurable, advanced computeritis".

See:

http://downlode.org/Etext/power.html

and

http://en.wikipedia.org/wiki/The_Feeling_of_Power

-- Yekta