Measuring with the body

Deepa is eleven and lives in a town in Haryana. When she gets a new uniform, her mother asks the tailor to make it longer by char angula: four fingers' width.

Deepa and her friends Anish, Hardeep, Padma and Tasneem start talking about how people measure with their bodies. Hardeep's grandmother measures cloth by the length of her arm. A farmer counts his strides. People use the length of their feet, a fist, or the width of their fingers.

The five friends measure their classroom table with their handspans (Deepa's mother calls it balisht). Their answers are not the same!

• Padma: 13 handspans
• Anish: slightly more than 13
• Tasneem: slightly less than 13
• Deepa: between 13 and 14
• Hardeep: 14

When they put their hands side by side, they see why: their handspans are different sizes. One table, five answers.

A measurement has two parts: a number and a unit. In "13 handspans", 13 is the number and the handspan is the unit. The unit gives the number its meaning: 70 on its own is just a number, but 70 kg is a weight, 70 m a length and 70 seconds a time.

A handspan, a foot, a fist or a finger is different from person to person. So we need a unit that gives the same answer for the same length, whoever does the measuring.

India has a long history of measuring. Ancient Indian books name units such as the angula (finger width), multiples of the angula, the dhanusa and the yojana, used to measure objects, buildings and towns. Carpenters and tailors still use the angula today, and objects with ruled markings that may have been scales have been found at Harappan sites.