Namaste

Weighing scales have become very high-tech devices. From bathroom scales with Wi-Fi connections to ultra-precise devices used in research or industry, modern scales are able to provide very accurate measures almost instantly. This has not always been the case, however, and today we take a look at the different systems that emerged over the millennia.

Weighing scales are born of necessity. As trading developed during the Antiquity, merchants needed a way to assess the value of goods that could not simply be counted by the pieces, like irregular-shaped gold nuggets, for instance. The most ancient relics of a weighing scale have been discovered in the Indus River valley, near present-day Pakistan, and date back to around 2,000 B.C. Those first weighing scales were actually balances, using two plates attached to an overhead beam, itself fixed on a central pole. The measurement was taken by putting the object measured on one plate and weight-setting stones on the other, until equilibrium was reached.

A total of 558 weights were excavated from Mohenjodaro, Harappa, and Chanhu-daru, not including defective weights. They did not find statistically significant differences between weights that were excavated from five different layers, each measuring about 1.5 m in depth. This was evidence that strong control existed for at least a 500-year period. The 13.7-g weight seems to be one of the units used in the Indus valley. The notation was based on the binary and decimal systems. 83% of the weights which were excavated from the above three cities were cubic, and 68% were made of chert.


Weights and measures are mentioned throughout the religious and secular works of the Vedic period in India. Some sources that mention various units of measurement are Satapatha Brahmana, Apastamba Sutra , and the Eight Chapters of the grammarian Panini.

The Arthashastra offers a wealth of evidence for the wide varieties of standardised weights and measures of the time. Officers were appointed to control their use and standardisation. The measurements include those of length, divided into several series, rising from those below the standard angula, defined as the ‘middle joint of the middle finger of a man of average size’; to those above, including the span and the cubit, and ending with the rod (danda) or bow (dhanus) of around 180 cm; and above this measurement of longer distance, the goruta or krosa and the yojana. Various special measurements are mentioned, for instance for digging moats, making roads or city walls. Measurements of capacity were set on different standards, for revenue, trade, payments, or palace purposes: these were applicable for both liquids and solids. Weights, too, were in several series: for precious substances there were three, for gold, silver, and diamonds; another series was for weights and general purposes. Weights should be made of iron or of stone from the Mekhala hills. Considerable attention is given to the types of weighing machines employed: one is a balance (tula) with two pans, for which ten different sizes are recommended for weighing different quantities; and another a sort of steelyard, in two sizes. A steelyard is used as a symbol on the negama coins from Taxila, suggesting their clear mercantile connotation. Equal attention is given to the measurement of time, based on the device named the nalika, being the time taken for one adhaka of water to flow out of a pot through a hole of the same diameter as that of a wire 4 angulas long, made from 4 masas of gold.

Depiction of equal arm balances is found in the art of Ajanta Cave no . 17  in the Maharastra state. Beams of steelyard balances have been unearthed from the 8th century CE archaeological sites at Sirpur and Arang.

The most modern body scales rely on electronics to measure the weight of their users. By sticking electrical resistances on deformable materials and running a current through them, it is possible to detect variations in the conductivity of the resistances that are correlated to the amount of pressure exerted on the material, and thus to deduce the weight of the person (or the object) standing on the scale. The most high-end body scales also act as impedance meters, and are able to calculate the ratio of fat mass and lean mass in the body. The impedance measurement is taken by generating a very small electrical current on the surface of the scale and measuring the resistance encountered by the current as it travels through the body. Lean mass is a better conductor than fat mass, so it is therefore possible to deduce the ratio of both in the body.

Namaste

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