We recently had a chance to visit this website with some pretty good little tricks for general aviation pilots.
We all know it is very easy to make a mistake in aviation when numbers are involved. Todays flight computers and glass cockpits provide us with a plethora of numbers to help us do our job, and provided we are able to cross check them, this is quite useful. When it is not so useful is when the numbers are wrong due to a wrong entry or malfunction and we don't recognize the problem.
This website is a collection of mental math tricks to get a rough answer while flying and to crosscheck the answers given by a flight computer or GPS. All the tricks are roughly organized into the tabs above based on what phase of flight you might first use them.
Give this site a read, and you just may end up bookmarking it!