1. An apparatus to design a circuit, comprising: a cell module comprising modeling information for a buffer cell, wherein the modeling information comprises a variable which enables the buffer cell to be modeled with varying amounts of capacitance based on the value of the variable, wherein further the variable may be set to a first value which enables the buffer cell to be modeled as a wire with substantially no characteristics of a buffer, wherein further the variable may be set to a second value which enables the buffer cell to be modeled substantially as a buffer; and a response module to calculate different model values of the buffer cell in response to different values of the variable.