Starter Option 2

Rule of thumb (or wrist, fist, neck, foot, and more)

You've heard the phrase rule of thumb, which nowadays means a practical but not very precise way of estimating something. Measure the height of a two-year-old boy, double it, and that's how tall he will be when full-grown. With one hand hold the corner of a piece of fabric at your nose and with the other hand pull out a length until that arm is fully extended, you'll have one yard. Pace out across an open space starting with your right foot and each time your left foot touches the ground you will have covered five feet.

They're all the same kind of thing; probably you can think of many others. But why call them rules of thumb? Well, because thumbs have been used to measure or estimate things for a long, long time.

Consider this case: the 18th century novel now known as Gulliver's Travels was orginally published with the title Travels into Several Remote Nations of the World by Lemuel Gulliver. One of the four voyages brought Gulliver to Lilliput, the land of tiny people, and the people were shocked and amazed by Gulliver's huge size. The Lilliputians manage to tie down Gulliver and one of the things they do is measure him, to have a good record of actual size of the giant in their midst. They measure around his thumb, what we might call the circumference; then they measure around his wrist. And they record Gulliver's wrist size as "two thumbs 'round."

Using the thumb as a unit of measurement was not totally made up by the author of Gulliver's Travels, Jonathan Swift. There are folk sayings in many parts of the world that say something like "Twice around the thumb, once around the wrist" or "Double the thumb for the wrist."

Other body parts

The rule of thumb size and wrist size gets extended to other body parts as well. The extensions include:

Twice around the wrist, once around the neck. In other words, double the circumference of your wrist and you'll have the circumference of your neck.

Twice around the neck, once around the waist. Double your neck size to find your waist size.

Once around the fist, once along the foot. Measure the circumference of your closed fist and you'll know the length of your foot.

Check it Out

To do this assignment you'll need some string and a scissors or knife to cut it.

Start with a thumb and wrist check:

a) Hold one hand with your thumb pointed up and fingers open. With one fingertip of your other hand press straight in on the palm side of the thumb. Start above the place where your thumb seems to meet the palm. Be sure to keep the thumb pointed up. Push in gently, then move down a little bit and push again. Find the spot where your whole thumb just naturally flexes in and down. To your finger, that spot will feel hard toward the thumb and soft below that.

1. Measure from that spot to the end of your thumb with your string. Measure more than once if you want to. Then cut the string so you have a piece the length of your thumb.

1. Now do the wrist above the same thumb that you just measured. Find the knobby bone on the outside of the wrist, up from your little finger.

1. Using string again, measure your wrist going around over that bone. When you're satisfied with the measurement, cut the string so you have a piece the circumference of your wrist.

1. Compare the thumb string and the wrist string. The rule of thumb says the wrist string will be twice the length of the thumb string. How accurate is the rule for you?

Keep some notes about what you find to use in the summary you write for this lesson.

Now check out one more rule of thumb. Use string or anything else that you decide will do the job. Pick one of the following or use another rule of thumb you've heard. You will have to write your own summary of how you do the check, so you might want to make some notes as you go along.

1. Twice around the wrist, once around the neck.

1. Twice around the neck, once around the waist.

1. Once around the fist, once along the foot.

What to send in:

Summarize what you found in the thumb and wrist assignment. Be sure to explain how well the rule of thumb worked for you. And describe any problems you ran into, for example deciding where to do the measuring.

For the second example describe the steps you followed and then report how well the rule worked for you. If the rule didn't work, tell what would help explain that.

Finally, tell how this checking out could be done more precisely.