## Monday, November 16, 2009

### Just the facts, ma'am, just the facts

Some of us have an obsession with the basic facts.
• Tell me what's in this food - give me the ingredient list PLEASE.
• I don't want any sodium laurel sulfate in my shampoo, thank you very much.
• I'd prefer the Insider Edition of the nightly news, if you don't mind.
• Give me the raw data, I'll be the one to judge whether I do X or Y with it.
And so on. But what "facts" really make sense? Do numbers always help us? Not always...

TODAY'S MATH BLOG ORIGINS
This morning my wife left the house for school. She reappeared 2 minutes later.

The Volvo says Low Coolant. Stop Engine. So I stopped the engine, what do I do next?

This is when you give her the keys to your car along with a kiss, and say thanks!

She did what the car asked! Notice the car didn't provide many facts. Just advice. Since it was cold outside, the car thermometer said 42∘F, and the engine had just been started, I was pretty sure it hadn't overheated.

If the car was just giving me facts, it might have said this:

Engine Coolant Level is 6.2 Liters

Does that help anyone? It wouldn't help me or my wife, even though now (after looking it up) I know the capacity is 7.2 liters. I don't know if being down a liter would matter. What we really want to know is what to do with the facts. Here are some symbols with words. These also interpret the facts:

Notice these thermometers show engine temperature. They don't tell me if the engine coolant is low or not. They don't even really tell me coolant temperature, or make a prediction. They just report a range. I created some more informative symbols which are shown below. Notice they have temperatures too.

The pictures above are theoretical. Here are some real indicators:

The instrument cluster picture shows me that the car is at normal operating temperature. The sub-dial below the tachometer displays engine temperature.

The pictures on the right show two possible displays for a Volvo. Notice the left one actually shows temperature in degrees. However, there are some issues. It is missing the red zone, which to most people would indicate overheating. And 300° F seems a bit high, since boiling is 212° F.  This dial could only work in the US, because the rest of the world shows temperature in Celsius. The right dial is more universally applicable.

Just as an aside,  20 years ago I was on a committee of ISO, the International Standards Organization. We were charged with deciding on the information and warning symbols that would appear on all vehicle dashboards. Here are a few of those warning symbols.

These symbols do not give the driver facts, they simply indicate something is happening in the region of the car that involves oil, or temperature, or electricity. The red implies something WRONG is happening. Back then I argued that an oil can with a drop of oil showing means virtually nothing! Given the computer processing power our cars have, we could easily display:

The oil level is too low. If you don't stop now it will cost you \$2500 for repairs!

I believe that would catch most drivers' attention. And they would stop. But Volvo chose a simpler approach that worked perfectly in our case. It gave a clear message before any damage was done.

Low Coolant. Stop Engine.

What is the morale of the story? When driving maybe I don't want math. Just keep me and my car safe.

JUST SAVE MY BACON, DON'T CONFUSE ME WITH THE FACTS

I added a liter of water, for the first time in 50,000 miles. The message went away and I drove to work.