Quote Originally Posted by benkeller3 View Post
Marv...
I like everything you do but sorry on this one. I am taking out my cellphone with the mm to inch and inch to mm converter
The real thing to take away from my post is how I adjusted the correct calculation into a calculation that could be done mentally without too much difficulty. I chose metric-to-inferial conversions as examples that would be frequently useful but the real hint is in the math tricks, not the problem on which they are used.

If you're already comfortable with math, the tricks won't come as any great revelations. OTOH, my experience on DIY fora suggests that math facility is not terribly common so tricks may be appreciated.