Illustration of the steps necessary for measuring the bias function, f. Left: the smoothed linear density field and the initial (Lagrangian) locations of a set of tracers – here the most bound particles of haloes with M_200b ∼ 2 × 10¹⁴ h⁻¹ M_⊙. Center: Distribution of the linear densities at the tracer locations (orange histogram) which is biased relative to the distribution at random locations (blue histogram). Right: The bias function, which is inferred by dividing the orange histogram by the background distribution. The solid lines show different bias models out of which the Gaussian bias model describes the data clearly the best.