Confirmation of correct ETT placement is currently performed by several methods. In the operating room, simple measurement of the length of the tube at the corner of the mouth using marks on the ETT is the usual method (Measurement Method: MM; 21cm at the teeth for women; 23cm for men). It is simple and rapid, but not reliable. One study attempted to improve on this by using anatomical landmarks to determine ETT tube length as measured at the mouth. It enabled a reduction in the incidence of too-deep placement of the ETT from 58.8% to 24%. Measurement of these landmarks is sufficiently inconvenient that it is not widely practised.