The problem of relying on Δ-values to call features. An example showing the problem of using Δ-values to decide the d-value cut-offs. The x-axis indicates d-values and the y-axis indicates Δ-values. (b) is the blow-out of the dashed rectangle region in (a). Two d-value cut-offs are indicated by the solid arrow and the open arrow respectively in (b) (see main text for a detailed explanation). The solid arrow marks the negative d-value cut-off τ− corresponding to the Δ-value indicated by the black line.