Personal Ruler

a) Begin with students creating two points A and C on a plain page. Make the line segment between them.
b) measure the line segment in inches and in cm.
c) put a third point B between the first two points. Measure the segments AB and BC, in inches and cm.
d) show that AB+BC=AC if the units match.
e) How to make a personal ruler:

1. Choose a school-approved body part (of your own).
2. On a long strip of paper ( I use cash register tape), mark a zero. Use a line across the paper, like a ruler.
3. Put one end of the body part at the zero: make a mark at the other end.
4. Repeat.
5. Label your marks 0, 1, 2, 3, 4, 5, 6, etc.
6. Find half the part, and mark along the lengths.
7. Find ¼ of the part and mark along the lengths.
8. Decide on a name for your measurement unit.

Now identify and measure 5 items in the room in inches, in centimeters, and in your personal units.
If there is time, practise converting between units.