In this ideograph, three is given as the approximate value for the mathematical constant pi (π).
Mahadevan's sign number 8218 is comprised of three elements. Firstly, there is a curved line, which represents part of a circle. Secondly, there is a straight line, which joins the two ends of the curved line, and represents the diameter. Lastly, there is a straight measuring rope, which has marks set on the diagonal, indicating a measurement of approximately three units.
Pi is the ratio of a circle's circumference to its diameter. The value of pi can be computed with varying degrees of accuracy, but it is correct to say that it is approximately three.
Illustrative Text Reference:
Kalibangan: Graffiti on pottery: K-104 A: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 322: Collections in India: Suomalainen Tiedeakatemia.
Comments:
There is only one extant example of this Indus sign.
K-104 is a two character inscription. The second character is the verb to carry. This is interesting because of the etymology for the English noun circumference, which is derived from the Latin verb circumferre. Circum means all around, and ferre means to carry.
Image Credit:
Indus Script Sign Number 8218: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.