Suppose a seller points to a rigid metal bowl and offers four filled measures of rice for 800 rupees. The parties know which bowl is used even if nobody knows its litre capacity.
The reference is this bowl, not any bowl later selected by either side. Substituting differently sized containers would undermine the agreed measure.
A reliable, demonstrable physical standard supplies the necessary identification.
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Kitab al-Buyu: Grain Sales, Bulk Heaps, Qafiz and Unit Prices
Suppose a seller points to a rigid metal bowl and offers four filled measures of rice for 800 rupees. The parties know which bowl is used even if nobody knows its litre capacity.
The reference is this bowl, not any bowl later selected by either side. Substituting differently sized containers would undermine the agreed measure.
A reliable, demonstrable physical standard supplies the necessary identification.