Wear prognosis method and maintenance method

A method of determining wear for an earth working machine having at least one earth working tool, the method comprising:

• prior to an earth working operation of the earth working machine:
• sensing one or more position values corresponding to a current tool contour of the at least one earth working tool;
• determining a first wear state by comparing the one or more position values of the current tool contour with a reference tool contour aligned therewith;
• and
• during the earth working operation of the earth working machine:
• continuously determining an actual work output of the earth working machine from one or more machine parameters;
• determining a second wear state of the at least one earth working tool, based on a calculated change in wear from the first wear state corresponding to the continuously determined actual work output and a material property of a corresponding substrate worked since beginning the earth working operation;
• predicting a remaining work output until a third wear state of the at least one earth working tool, based on an expected change in wear from the second wear state corresponding to a material property of a substrate yet to be worked during the earth working operation.