How Many Kaldarsi for a Seer?

The bane of historians are those local accounts that excitingly proclaim "the famine was so severe that a seer of wheat cost fifty kaldarsi!" But never report the ordinary price of wheat. These accounts simply assume that everyone already knows this, along with how much s seer weighs and a kaldar is worth.

--Thomas Barfield, Afghanistan: A Cultural and Political History (2010)

Barfield is about as well qualified to write a history of Afghanistan as anybody in the planet. He first worked in Afghanistan a generation ago, and he has spent most of his career studying the interplay between what Ibn Khaldun* called "desert" and "sedentary" civilizations: Barfield's Perilous Frontier is the best thing I've read on the interplay between China and its northern neighbors.

In contrast to the seer/kadarsi problem, Barfield cites appreciatively works that "retain their value centuries after they were written precisely because they cogently analyzed what other interlocutors took as boringly self-evident." He offers the inevitable example of de Tocqueville, and also Mountstuart Elphinstone's Kingdom of Caubul.
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*That man again.