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When I met my husband, I was head over heels for him.  He was sweet, smart, an engineer…little did I realize how the engineer stuff leaks into your everyday life.  One day early in our marriage, he says to me, “We need to go to the store to get a little notebook for your car.”

“We need to track every time you fill up how many miles you are getting and then also have a place to record when we change the oil or do any work on the car,” he replied like everyone did it.

In my head I am thinking, “Crazy!  A little OCD…don't you think?” but because I was so in love, I went with it.  (I am still major in love, just more willing to stand my ground these days when engineering interferes with being practical)

It took me almost 6 months to get the hang of it.  As I kept this car journal, I started to see the beauty of knowing what my gas mileage was.  There were times we could see that maybe we weren't getting the best mileage and we would pop the hood to see what needed to be changed or fixed.

There it is!  The notebook.  This notebook has been with us since 2005.  I could hardly believe my eyes!  It's been awhile since I had opened and flipped through all of the pages.  Each page was recorded so simply.  The date…odometer reading…mileage for this tank of gas…total gallons filled up.

On this first page, you can see that we had to replace an air filter and then also the oil and air filter.  From oil change to the next was a little over 8,000 miles.  Waaayyy more than the manufacturer recommends.  Some years our car was more tenderly cared for than others.  Let's look and see if we can calculate the average miles per gallon.  I am going to look at the third line.  I use the gallons on the second line because that is what the third line was driving on.  Does that make sense?

394.2/ 20.14  = 19.61 miles per gallon

If I want, I could find the average for this entire page by adding up all of the miles and totaling it, then adding up all of the gallons and totaling it.  Then we'll divide.  Let's see how close we get to the average on line three.

4719.1/278.54 = 16.9 miles per gallon

There is lots of ways we could analyze the data on this page.  How many days between fill ups?  How many gallons on average do I put in?  What is the farthest I've driven on one tank of gas?

Because we have this car journal, we are able to estimate when we were going to need to replace tires, change the oil, or be aware that something might need repair before it does any significant damage.  This gives us peace of mind because we could actively save for an emergency or repair because we knew what our cars habits were.  In fact, the fuel gauge inside the gas tank busted.  Our car still worked, we just didn't have a nice gauge to tell us when to fill up.  Now we rely heavily on this notebook and our odometer to tell us when it's time to fill up and because we know the average amount of miles we can get out of a tank, we know when we've got to gas up.

## Car engineers and manufacturers

They have to provide the public with all kinds of fancy information about cars.  In fact, the math and science behind miles per gallon and how it relates to a cars performance is so exact, they can program it right into a car and alert the driver when it's time to get the oil changed or stop and get some gas.

## Public Transportation

Budgeting for gas to move a population takes a lot of data and care that allows them to predict and prepare for repairs and changing routes to save money.