The intercept on the vertical k obs axis can be found by setting [I] 0 = 0 in Eqn and simplifying the resulting square root expression to obtain k obs = k off + k on [E] 0 . Note that under classical, as opposed to tight-binding, experimental conditions the intercept on the vertical axis is at k obs = k off , according to Eqn . In other words, tight-binding simply shifts the Y-axis intercept upward by k on [E] 0 .