During an MSNBC town hall last night, Hillary Clinton seemed to pledge that if she’s elected, half of her Cabinet will be made of up women. Host Rachel Maddow asked her about Canada’s prime minister, Justin Trudeau, who promised to make his cabinet half women after he was elected last year (when asked why he took that step, Trudeau said, “Because it’s 2015”). Clinton responded, “I am going to have a Cabinet that looks like America, and 50 percent of America is women.”

That might sound not quite like a hard and fast promise, but if Clinton follows through, it would be historic. Just how historic? I thought it might be worth placing this question in context, so I did a little number-crunching on the history of the president’s Cabinet.

Four of the Cabinet secretaries have been around since the beginning: the secretary of State, the secretary of Defense (more straightforwardly called the secretary of War back then), the secretary of the Treasury, and the attorney general. Over time, more were added (and some removed), and today we have 15 Cabinet departments. We also have Cabinet-rank positions, like the administrator of the Environmental Protection Agency and the director of the Office of Management and Budget, but for the purposes of this analysis I’m going to exclude those.

Between 1789 and 1933, when Franklin Roosevelt made Frances Perkins his secretary of Labor, every single Cabinet secretary was a man. After Perkins left office in 1945, it would be another 30 years before another woman was made a Cabinet secretary, when President Ford appointed Carla Hills to be his secretary of Housing and Urban Development. Since then things have gotten somewhat better for women at these top levels, but we haven’t reached anything approaching equity.

Now let’s look at some numbers. I’ve included both the total for people who have served as Cabinet secretaries, and the number of years women have served, since it’s more significant if someone is a secretary for eight years than for one. First we’ll look at a table, then I’ll put it in graphical form, since everyone loves graphs:

Just a note: I’ve included any year in which a woman served, but I have excluded all the times when a secretary served for the first few weeks of the year before a new administration took office. In addition, thirty-four men and two women have held multiple Cabinet positions; I’ve counted them once for each position they held.

In total, 29 different women and 509 men have served as secretaries of these cabinets over the course of American history. The best-performing department in terms of gender equity is Health and Human Services, where six of its 22 secretaries since it began in 1953 as the Department of Health, Education, and Welfare have been women. And in 24 of the 64 years of the department’s existence, it has been led by a woman. The worst are Defense and Treasury, which have never been led by a woman in 228 years of existence, and Veterans Affairs, which hasn’t been led by a woman in all its time, but has only been a Cabinet-level department since 1989.

Now let’s look at this graphically:

As you might expect, things have gotten a little better in recent years. Eight of the 33 Cabinet members Barack Obama has appointed were women, or 24 percent. For George W. Bush it was six of 34, or 18 percent. For Bill Clinton it was five of 28, also 18 percent. But nobody has even approached 50 percent.

So if Hillary Clinton does actually bring gender equity to her Cabinet, it will be something positively revolutionary. And who knows, she might even let a woman lead Treasury or Defense. That’s more than a bit overdue.

* The graphics included in this blog post have been corrected. There have been three female secretaries of state, serving a total of 12 years.