The nation's unemployment rate is low. Monthly job gains are high. By all official measures, the US economy is in recovery mode. Not in Donald Trump's world.

"We have a real unemployment rate that’s probably 21%," Trump Time magazine this week. "Our real unemployment rate — in fact, I saw a chart the other day, our real unemployment — because you have ninety million people that aren’t working. Ninety-three million to be exact. If you start adding it up, our real unemployment rate is 42%."

Trump's inventing some new numbers, but this isn't a new line of attack from him: He's been openly skeptical of the government's job reports for years.

When I spoke with the Trump campaign earlier this summer, Trump maintained that the "real" unemployment rate was 18 percent. (Like so many Trumpisms, the number's gone inexplicably up.)

It was hard to accept Trump’s claims then. But it’s even harder now.

The official unemployment rate is based on a monthly sample of households, which tracks how many people have a job, who's "actively looking," and who's waiting to get called back after a recent layoff. And by this traditional measure, US unemployment has steadily plunged, from 10 percent in October 2009 to 5.3 percent in July 2015.

An alternative measure of unemployment, called U-6, measures Americans who are not just unemployed but "underemployed" — they've settled for part-time jobs — or have given up looking altogether. The U-6 unemployment rate soared past 16 percent during the economic downturn, and it's still pretty high. According to the most recent U-6 calculations, about 10.4 percent of Americans are unemployed or underemployed. Some critics of the White House's economic policies say that's the number we should be using.

But both of those figures are far from the numbers that Trump invoked.

So how did Trump arrive at 42 percent unemployment? Probably by relying on a different number called the labor-force participation rate. That ratio measures the percentage of the population that's older than 16 and actively working.

According to the most recent report, about 37 percent of Americans older than 16 aren't working. Factor in Trump's tendency toward exaggeration, and that's pretty close to the number he quotes to Time.

Keep in mind: No one judges unemployment this way. No one should judge unemployment this way.

Trump's number includes the tens of millions of Americans who actively choose not to participate in the labor force. He's counting high school and college students. Elderly Americans who chose to retire. The disabled.

Even if Trump gets one point technically right — there are about 93 million Americans over age 16 without jobs — we don't want all of these people to be working. (Unless you're a fan of conscripted labor.)

And that's why this isn't a honest way to assess the job market.

What Wall Street thinks of unemployment

It's worth reiterating: No one of any significance agrees with Trump's numbers. Not even the business community.

I recently looked at Wall Street firms — analysts who specialize in tracking hiring patterns, and leaders of companies like Monster.com. People whose job it is to know how many jobs there are.

In all cases, these firms either trust the government's numbers or have their own proprietary data that show massive declines in unemployment.

According to proprietary research from Indeed.com, which bills itself as the world's largest job site, demand for labor has dramatically improved.

"In 2009, during the midst of the recession, the job market looked bleak with 6.2 unemployed job seekers for every opening," Indeed's researchers recently concluded.

"Today, economic conditions have improved with 1.7 unemployed job seekers for every opening and unemployment below 6% for the first time in six years."

So it's worth remembering: When Donald Trump disputes unemployment numbers, he's not just taking on Obama. He's disagreeing with Wall Street.