Poka yoke is a Japanese phrase meaning mistake proofing. Poka yoke is meant to shape behavior at the level of execution. There are two approaches to this. One, is to prevent humans from making a mistake, to physically prevent it. If it’s not possible to prevent the mistake, you can use poka yoke to anticipate and warn of mistakes. Perhaps the easiest way to understand poka yoke is to see some examples. There are many applications of mistake proofing. Many of them are related to safety. A microwave oven will not operate if the door is open. Rumble strips on the highway let you know if you're wandering off the road. And speed bumps cause you to check your speed. Can you guess how these prevent errors? If you've ever painted a white ceiling you know that it's extremely difficult to see if you have missed any spot because you're painting white over white. Later, when the light changes you can see your mistakes. Glidden makes a ceiling paint that goes on pink, making it easy to see if you've covered everything, then when it dries it turns white. Do you know why manhole covers are round? That's the only shape that cannot possibly fall in the hole. Most sinks have small slots or holes at the front or the back near the top. Their purpose is to prevent overflow if you leave the water on. In developed countries, many restrooms have motion sensitive lights and commodes. The lights are not on except when needed, saving energy. And commodes flush automatically. In manufacturing, most machine are well-guarded this days. Injection molding machine, for example, have mechanical, hydraulic and electrical interlocks, they're all engaged prevent the machine from working when you slide open the door. There are lots of examples for poka yoke in computer programs. Online forms can verify that all the required fields have something in them. They can verify data types and values. There are many different ways to reduce or eliminate errors when you're asking for data to be input. In the early days of data entered online, you might see something like the top example here, asking for a phone number, which obviously can be formatted a number of different ways. The next step in the evolution was the second one with the same box, but an example of how it ought to be formatted. Today, most systems will have something like the third example. Where there is only enough room for the necessary digits that can only be put in one way. This is an insertable piece of tooling for a stamping die. In the original design on the left, the piece can be put in backwards. An error that could costs thousands of dollars worth of damage. The redesign on the right makes it so the tooling can only go in one way. This is a novel poka yoke to ensure that bolts are tight. There's a washer with bits of plastic on it that goes under the head of the bolt. When the bolt is properly tightened, the plastic squirts out. A bridge inspector would previously have had the use of torque wrench to check the tightness of the bolts. Here, you can see at a glance that all the bolts are tight except two. This is a common jock for phone or Internet. The tab marked B keeps the connector from being inserted upside down. The tab marked A Is designed to protect tab B and keep it from being broken off. This container handling equipment has a subtle feature that keeps containers from rolling off the platform prematurely. Two yellow tabs flip up when the platform is raised. The tabs have weights on their lower half. When the platform is down, these weights are pressed up by the body of the vehicle below the platform. They are there when they're needed and gone when they're not. Knowledging in the world is information that's embedded and coded or implicitly resides in the components of a task. Here, the shape of the dipsticks communicates their purpose. The yellow dipstick is shaped like an O and is used to check the oil level. The orange dipstick is shaped like a T and is used to check, you guessed it, transmission fluid level. It's ironic that this design is very language-specific but comes on a Japanese brand. New lawnmowers are required to have a safety bar in the handle. They must be pulled back in order to start the engine. If you let go of the safety bar, the mower blade stops in three seconds or less. This is a medical example. A tube is inserted into the patient's lungs. But how did you know if it is the right place, in the lungs, not the stomach? Squeeze the plastic bulb and then put it on the tube. If the bulb inflates with air, the tube is in the lungs. If not, then an error has occur. This final example has three poka yoke's designed in. In countries where they drive on the left side of the road, visitors can get confused. Offset crosswalks, and accompanying railings, forced pedestrians to turn and walk toward oncoming traffic. So they can see what's coming. Instructions printed on the blacktop, or curb, say, look left, to direct pedestrian vision in the proper direction. And the jagged lines warn drivers that they're approaching a crossing