Reverse the quotation direction
Assume GBP/AUD moves from 2.00 to 2.20 AUD per GBP, a 10% increase. Its reciprocal moves from 0.50 to approximately 0.454545 GBP per AUD. The reciprocal's percentage change is about −9.0909%, not −10%. These are arithmetic examples, not position returns.
Locate the asymmetry
For a fractional change r, the reciprocal changes by 1 / (1+r) − 1. At r = 0.10, that is 1 / 1.1 − 1. The denominator changes, so the magnitudes differ.
Recovering an earlier level
A fall from 100 to 90 is −10%. Returning from 90 to 100 requires approximately +11.111%, because the second calculation starts at 90. Adding percentage changes without respecting their bases creates the same kind of error.
Document the calculation
Write the symbol, units, start, end and denominator. Try 2→2.2 and 0.5→0.4545454545 in the worksheet. Retain input precision and round only the displayed result.
Respect the boundary of the example
No contract size, margin, account currency or fee is included. This calculation explains quotation direction, not the profit or loss of a leveraged position.