If you are heating plates of metal, what happens if someone puts on a plate that is twice the mass of the average one? Or one that is made out of aluminum instead of copper? You could add a weight sensor to the system, but what if the difference is in the shape instead of the weight? A tall, skinny piece of metal will have different heating charac- teristics than one that just matches the surface area of the heater. There are similar problems with other control mechanisms. An automo- bile cruise control, for instance, has to handle things like headwinds, uphill and downhill grades, and the decrease in horsepower caused by turning on the air conditioner. A proportional control system would have problems with these conditions, since the right amount of throttle to apply going uphill in a strong headwind is different from the amount needed under the opposite set of conditions. PID Control A control method that handles conditions like this is called PID (Propor-
And whatever someone else has done, you can probably do as well. There are few limits. This is not an easy rule, but it is definitely simple. You, too, can learn anything you need to learn to accomplish any goal you can set for yourself. Once I learned this idea, I was unafraid to change jobs, and even industries. I learned how to sell advertising, investments, automo- biles, and office supplies. I worked in real estate sales and leasing, 77 ccc_tracy_5_77-89.qxd 6/23/03 2:47 PM Page 78 78 ➤ CHANGE YOUR THINKING, CHANGE YOUR LIFE and then real estate development. Then I engaged in importation and distribution, then banking, printing, consulting, and eventually speaking, writing, recording, and corporate training
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