: Why NOT convert to metric?.

To change to decimals is easy, basically you don't have to do anything except use the numbers differently (easier), however a full blown change to metric is MUCH harder.

I read a real good article about this subject in a science magazine recently and it was based on the metric-english unit conversion mistakes that crashed the lander on mars (or maybe it was a TV show, I can't remember).

Switching to metric is much harder than it appears.

1. It would take a few generations for the switch to be smooth. Teach the kids, phase in metric while the young ones use it, and then phase out the current system over time. It might be easy if you grew up with metric, but if you're used to the price of a gallon of gas, or how far a mile is etc..and suddenly they are selling gas in liters and using distances in kilometers it won't mean anything to you.

2. I work at a big airplane manufacturer. Now imagine that all of the fasteners are sized in fractions of an inch. All of them would have to be converted and wouldn't work out to normal metric fastener sizes. If the fasteners were to be switched to a metric size, there would have to be more or less of them in a given pattern to carry the same load. So basically all of the drawings would have to be changed over and many of them re-designed. Do you know how much money it costs to design an airplane? Somewhere in the Billions. Then there are the tools that would have to be changed to match the new designs etc... Oh, and what about the skin thicknesses that are in thousanths of an inch, they would have to be converted to new standard sheet thicknesses.
Sure, the auto companies switched, but they are building completely new models every decade or so. The 737 and 747's are still being built today and although there have been a lot of upgrades, much of the structure is still the same since the 1960's. It would be a major change.

If a new airplane were designed under the metric system, and the old ones were using the english units, imaging the many possibilities of mistakes in the Engineering departments that work on more than one airplane.

3. Then there's the airplane pilots that insist that altitude be measured in 100 foot increments. If they convert to meters a 100 meter increment is only about 1/3 as fine as a 100 foot increment. I see a hard landing coming. Are they going to start measuring in 30 meter increments (do the math on that every time you want to do a calculation)

4. One degree F change is about the fineness that a human can feel the difference in temperature. There are 180 degrees F difference between the freezing point of water and the boiling point. There is only 100 degrees difference in C.

Metric is not necessarily better in all applications, just easier because everything is in based on 10.

Now I am wondering why their isn't metric time (10 metric hours [deciday] to the day, 100 centidays to the day, and 1000 millidays to the day...etc). Would you still want to work 8 hours a day. Can you see how hard it would be for you to convert in your mind knowing how long an hour, minute, second is.