What a great day! Charlie and I got up early and took a long (for us) ride on the 
Norwottuck Bike Trail. We rode 10.4 miles altogether, starting at Station Road and riding to Pete's Drive In. It was a good first long ride of the season. When I replaced the battery in my cyclometer last year, it forgot the calibration which tells the computer how far each revolution is. It's possible to manually estimate the circumference, but I've lost the directions, so I don't even know what the units are. Instead, I noted the disparity at the mile markers and at 4 miles the cyclometer thought we had gone 7 miles. At Pete's, I went into the setup mode and found that it had 2155 as the circumference. I didn't have a writing utensil so I mentally cross multiplied 4 x 2155 and divided by 7. I decided that 1230 was close enough for government work (as my father-in-law would say). I check it as we were going back and it seemed pretty close. I was pleased when I used the calculator just now to see that the correct answer is 1231.429. Not too shabby.
The only thing remarkable about that is that I never really learned to do math properly. I couldn't be bothered to memorize math facts as a kid. I found this crippling in taking advanced math courses. If you can only get 80% of your basic calculations right, and each problem requires 2 calculations (like this one), then you can't get better than a 60% on the test. I understood math well enough and, if allowed to use a calculator, (or better yet, a computer), I might have actually excelled at math. Instead, I came to hate it and it was only after I graduated from college and worked as a cashier that I really learned the math facts well enough to do calculations in my head. As a graduate student, I took three semesters of graduate level statististics and loved it: it was taught from a conceptual standpoint where the focus was on understanding how the statistics worked, designing experiments and interpreting results properly.