I think what you want to be saying is that GDP is measured in constant monetary units, e.g., "1980 dollars" or "2010 euros".
That monetary equivalence equates to real purchasing power over goods and services. Nominal changes in currency values (whether foreign-exchange or inflation/deflation) are pencilled out in this way.
And the GDP growth that is measured is as a percentage in terms of those constant currency units. Which, again, reflect actual capacity to purchase material goods or the product of energetic effort.
