An incredible guide, on how to model with precision in Blender was released by Robert Burke. The guide is a PDF file with 151 pages! If you always find yourself in trouble, when you have to model anything with precision, this guide has some very good tips.
A real modelling project is used to demonstrate the techniques and precision tools. So, not only the tools are explained, but the whole modeling process with a real project! If you want to see it for yourself, visit this link to download the guide. It`s a PDF file with almost 5 MB.