"In the regression formula, we substitute the percentage change in the value of the asset to be hedged for yt, and the percentage change in value of the hedging instrument for xt"
However, in the following example, they use domestic-currency return on the portfolio as Y and use percentage changes in the spot rate as X:
RDC = α + β(%Δ_SGBP/CHF_) + ε
Is that a contradiction?