I am doing a lab which involves the determination of vapour pressure of a particular compound by Knudsen Effusion. Like other analytical methods it involves calibration but we are using the know vapour pressure of naphthalene because its in the accepted range. So we have an equation for the vapor pressure of naphthalene from literature and we are also performing a calibration in the lab. What I am not understanding is how to use the calibration curve in the form ln P= A-B/T (where P is the pressure, T is the temperature and A and B are constants) for naphthalene to calibrate the instrument for another compound. What is the purpose of using the equation from literature and then calculating it in lab ourselves?