Consider a hypothetical coin of 30% silver and 70% base metal exchanged for another coin also containing silver. Treating each coin as pure silver would be wrong, but ignoring the real silver components would also be wrong.
The analysis must account for the silver components' counterpart and the consideration for the non-silver material. This is a historical mixed-metal case, not a complete contemporary ruling on paper or digital currencies.
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How mixed components affect the analysis
Bab al-Sarf: Mixed Currency Exchanges, Debased Coins and Obsolescence
Consider a hypothetical coin of 30% silver and 70% base metal exchanged for another coin also containing silver. Treating each coin as pure silver would be wrong, but ignoring the real silver components would also be wrong.
The analysis must account for the silver components' counterpart and the consideration for the non-silver material. This is a historical mixed-metal case, not a complete contemporary ruling on paper or digital currencies.