market rate
相場 / market-rate — Measuring
The price actually being paid in the market.
1 Rupee of HyderabadAH 1335 (circa 1917)
Even if the system sets a ratio of 'one to fifteen,' if the market trades at 'one to sixteen,' the market is the correct one. Do not take the par value found in historical sources as the actual market rate of that era.