Today I read Numerology by David V. Barrett, a small guidebook that serves more as a brief introduction than as a thorough resource. I was unfamiliar with the Arrows of Pythagoras grid; the interpretations Barrett gives for such seem vague enough to be useless, however. The author advises the use of one's commonly used name when figuring out one's numbers, rather than one's name at birth -- I think it's worthwhile to check both. There's also a short section on colors and gemstones associated with numbers.