QuickMedical Questions: What's the Frankfurt Plane?

QuickMedical Question Guy:

What is the Frankfurt plane? I've also seen it written as Frankfort plane. What is the difference? Is there a difference? When I Google it I get lots of answers, some of which come from your site. So I thought I'd ask the Frankfurt plane experts. What's the Frankfurt plane?

Curious in Cairo (Illinois)

The Frankfurt plane is the same as the Frankfort plane. It's simple. It's this:

Easy right? Well, I suppose we could explain a little more. After all, if you're using the gold standard in stadiometers, you want to use the device properly. And to properly measure height, you must use the Frankfurt plane. Click ahead to read an explanation of the Frankfurt plane.

Established at the World Congress on Anthropology in Frankfurt, Germany in 1884, the Frankfurt plane is the agreed upon anatomical position of the human skull. It was decided by the World Congress that a plane passing through the inferior margin of the left orbit and the upper margin of each ear canal or external auditory meatus, a point called the "porion," was most nearly parallel to the surface of the earth, and also close to the position the head is normally carried in the living subject.

When measuring height it's important to keep the subject's head in the Frankfurt plane, along with other recommended body positioning for the specific device. Some measuring devices even have a Frankfurt line to assist in head positioning, like the Seca 274 Free-Standing Wireless Stadiometer.

Whether you're using a simple wall growth chart or the QuickMedical Heightronic 235A, keeping the Frankfurt plane is extremely important.

But why is it spelled two different ways? The older English spelling of Frankfurt the city was Frankfort. Because they are pronounced remarkably similarly, Frankfurt began to be used in English, as well, and is now the common English and German spelling. Frankfort is still used by some English writers throughout the English-speaking world. Glad you asked, Curious!