An exceptionally interesting, data-driven paper was just published in the US Proceedings of the National Academy of Sciences that suggests much was unique about the ancient Indus weight system: "To determine how different units of weight emerged in different regions, researchers compared all the weight systems in use between Western Europe and the Indus Valley from 3,000-1,000 BC. Analysis of 2,274 balance weights from 127 sites revealed that, with the exception of those from the Indus Valley, new and very similar units of weight appeared in a gradual spread west of Mesopotamia. To find out if the gradual formation of these systems could be due to propagation of error from a single weight system, the researchers modeled the creation of 100 new units. Taking into account factors such as measurement error, the simulation supported a single origin between Mesopotamia and Europe. It also showed that the Indus Valley probably developed an independent weight system."
"When plotted as normal distributions with a CV of 5.4%, the weight units of Western Eurasia are sharply divided into two groups (Fig. 3E): on the right side, the Indus unit remains isolated, while all other units between Mesopotamia and Atlantic Europe form a cluster on the left side, between ∼7 and 11 g. The error ranges in this cluster overlap to the extent that supposedly different units are in fact barely distinguishable from one another. In other words, large portions of the intervals that were accepted as valid units in one region were also accepted in another region with an allegedly different unit. This means that a single merchant could potentially travel from Mesopotamia to the Aegean, and from the Aegean to Central Europe, and never change their set of weights while simply relying on approximation. The same was not possible between Mesopotamia and the Indus Valley.
As weighing technology gradually spreads west of Mesopotamia, new units emerge along the way, slightly different from the closest preexisting ones but still largely compatible. At the same time, the strikingly unique Indus unit stands out not only numerically, but also geographically, as it is separated from Mesopotamia by a large void of documentation corresponding to the Iranian Plateau (Fig. 2A)."
Image 1: Examples of Western Eurasian balance weights of the Bronze Age. (A) Spool-shaped weights from Tiryns, Greece (photograph by L. Rahmstorf). (B) Cubic weights from Dholavira, India (photograph by E. Ascalone, Department of Humanities, University of Roma Tre, Rome, Italy). (C) Duck-shaped weights from Susa, Iran (photograph by E. Ascalone). (D) Parallelepiped weights from Lipari, Italy (photograph by N. Ialongo). Approximate scale.
Image 2: (A) Diffusion of weighing technology. The gradient illustrates the time scale of the spread of weighing technology as suggested by the archaeological evidence. The dots indicate the find spots of the balance weights included in the sample of the statistical analyses. The colors of the dots indicate the regional weight system to which they are assigned. (B) Chronology of the analyzed datasets.