Search Loci: Convergence:
Every mathematician worthy of the name has experienced ... the state of lucid exaltation in which one thought succeeds another as if miraculously ... This feeling may last for hours at a time, even for days. Once you have experienced it, you are eager to repeat it but unable to do it at will, unless perhaps by dogged work ....
The Apprenticeship of a Mathematician.
The Grounde of Artes by Robert Recorde
On this page there is an outline of the first dialogue in this book. (Recorde wrote his book in the form of a dialogue between student and master.) This dialogue deals with some of the elements of arithmetic, including the basic operations and the use of the rule of three (or the Golden rule).
A page dealing with various "rules of practice" in arithmetic.