Reducing changeover time of machines—the time it takes to switch from the last “good” part of product A to the next “good” part of product B—is one of the most powerful tools in lean manufacturing. The goal is to achieve “SMED”—Single Minute Exchange of Dies—in other words, bringing changeover time below 10 minutes. (Although "SMED" is perhaps the ugliest sounding acronym ever invented. It sounds like some horribly virulent disease. Or something that oozes from some body cavity.) Legendary consultant Shigeo Shingo introduced this concept to Toyota in the 1950s, helping them reduce the changeover time for some of their stamping processes from eight hours to less than 10 minutes.

The concept applies to any other process in which you need to make a change from one “product” to another. Turning over hospital operating rooms so that they can accept the next patient is one example. Changing tires on race cars is another example. (Here’s a mind-boggling video of the fastest Formula One tire change (1.92 seconds!) in history. And here’s a 21 minute analysis of how they did it.) Although we don’t think of people as products, hiring and onboarding new employees is actually another place where reduction in “changeover” time is important—what organization wouldn’t want a new employee to be fully ready to work on the first day of the job?

For an individual in an office, changeover isn’t visible the way it is in a manufacturing plant. But knowledge workers are constantly changing over the most critical piece of equipment: their brains. Any time people are interrupted in the middle of a task, they’re forced to execute a complex mental changeover (particularly when the tasks are vastly different). This task switching imposes a real cognitive tax on the worker, too—greater stress, and a longer time to complete the work. Gloria Mark, professor at the University of California, has estimated that after a significant interruption, people take about 23 minutes to return to the original task

Interruptions—even self-imposed “multitasking” interruptions—are costly, but there are ways to mitigate the damage, even if you can’t get down to a “single minute exchange of brain. 

One of the key tenets of SMED is to do as much prep work as possible before you stop the machine—in the language of manufacturing, you externalize preparation steps that can be done while the machine is running. For example, you might get all the tools and replacement parts lined up at the machine before stopping it. For a knowledge worker, that can mean having the information (files, emails, reports, etc.) for your next task already pulled out, rather than having to look for them when you switch. That’s pretty obvious. 

But a more valuable kind of setup externalization comes from simply knowing what it is that you’re going to work on next. There’s a real and significant “initiation” energy required to scan your to-do list and just decide your next task. We’ve all had that experience—trying to decide whether you should fill out your expense report, work on your annual peformance reviews, or call your mother-in-law back is an exhausting choice that usually results in you checking email, or getting a cup of coffee instead.

However, if you consciously plan and sequence your tasks—if you “pre-decide” your work—you reduce the cognitive burden of simply figuring out what to do next. You’ve essentially externalized one of the key elements of the changeover. And that allows you to make the changeover to the next task faster. 

You can do this in a few ways. You could use a personal kanban to show you what five things you’ll work on today. You could schedule the work in your calendar. You could simply lay out the files on your desk (but just the ones you’ll work on today). Or you could make a very short to-do list, with just the 3 or 4 things you’ll take on today. Or you could use phone apps or other software to help. 

This improvement may not seem like much. But if you could reduce mental changeover time by five minutes per day, that adds up to about 20 hours a year, which you can either spend doing something more useful for the organization, or just adding to a vacation on Maui.