Before an operation proceeds several tests are usually to be performed. These include, but are not limited to, a CT scan, pulmonary function tests, and cardiology exams (such as auscultation and ECGs).[3] After a CT scan is taken the Haller index is measured. The patient's Haller is calculated by obtaining the ratio of the transverse diameter (the horizontal distance of the inside of the ribcage) and the anteroposterior diameter (the shortest distance between the vertebrae and sternum).[21] A Haller Index of greater than 3.25 is generally considered severe, while normal chest has an index of 2.5.[18][22][23] The cardiopulmonary tests are used to determine the lung capacity and to check for heart murmurs.