This calculator uses a power model where the rider's power output is a quadratic function of their cadence. $$ P_F=P_{\text{max}}\left[2\left(\frac{\text{PR}}{\text{PR}_{\text{opt}}}\right)-\left(\frac{\text{PR}}{\text{PR}_{\text{opt}}}\right)^2\right] $$ The parameter $\text{PR}_{\text{opt}}$ is the optimal cadence for an individual rider and $P_{\text{max}}$ is the power output maintained at that cadence.