attached to the base underlying the slit when the gage is attached to a structure with a suitable adhesive and the structure is subjected to repeated loading a fatigue crack immediately begins at the inner end of the slit and increases in length as an approximately linear function of the accumulative fatigue damage strains incurred by the structure the crack in the gage occurs in advance of and independently of any crack in the structure itself application_number US 59191575 A description an embodiment of the fatigue damage indicator is shown in detail in fig1 and 2 it is seen in these views that the indicator has a metal base 10 which is nominally rectangular when viewed from the top and has a height a and a width b the height and width of the indicator are not critical to its function and can normally be chosen to suit the geometric requirements of a particular installation it is not even necessary that the plan form shape of the gage be rectangular it is only necessary that the gage have a sufficient height to provide an adequate amount of gluing surface as will be discussed below and that it have a sufficient length to accommodate the expected amount of crack growth the indicator was developed primarily with bases made of aluminum but the base can be made of.