1550 ISD
From ERPC Wiki Archive
The International Standard Dollar is a hypothetical currency with the same purchasing power parity (PPP) as the Nylander Daler at a given point in time, based on both the purchasing power parity (PPP) of currencies and the international price of commodities. It's used to make comparisons both between countries and over time. It provides a more accurate estimate of the standard of living than to using exchange rates alone.
The 1550 ISD is the most commonly used benchmark.