A method of positioning a virtual guide on a virtual model of a patient's scapula for installing a glenoid implant, the method comprising: creating the virtual model of a patient's scapula using software run by a processor, the virtual model created from an anatomical image of the patient's scapula; selecting at least a first point on an anterior rim of a glenoid fossa and a second point on a posterior rim of the glenoid fossa of the virtual model, the points displayed on the virtual model; and positioning the virtual guide on the virtual model of the glenoid fossa as a function of the first point on the anterior rim and the second point on the posterior rim.