BooksChildcraft: The How and Why Library, Volume 13. Chicago: World Book, 1989.
Mathmagic section was very useful because it had concise descriptions of cubit measures and illustrations for children.
Prior to this project, my first graders had done a number of activities involving measurement with non-standard units; Unifix or similar interlocking counting cubes, paper clips, etc.
To introduce cubits, we discussed how in ancient times, people measured things using their arms, hands and feet as measuring units. Because the lengths of these varied, people realized they needed a "standard" unit of measurement. In ancient Egypt, people used the distance from their elbow to their fingertips. We call that distance a cubit (from cubitum which is Latin for elbow). The ancient Egyptians may have been among the first people to use a standard measurement for length. Perhaps they went to the King and measured his arm, which became the royal cubit length used by everyone. This cubit measures about 21 inches (52.5 centimeters) by our standards. Cubit sticks could be made of granite. They could be subdivided into 7 palms (based on the width of a hand) and 28 digits (based on the width of a finger).
To help youngsters understand the need for a standard of measure, I sold "gold" (actually lengths of gold thread) to two different students for 25 cents. After each measured out their gold thread, they discovered the lengths were different, and they had not gotten an equal amount for their money.
We also built a structure that was five cubits high, using non-standard cubits based on individual students´ arms, and then were unable to put a roof over it because the walls were uneven in height.