Two experimental methods are described, used for studying the crack length increase, in dependence with the loading cycle’s number. The basis for both methods is the tension test, applied on compact specimens of annealed OLC45 carbon steel. The first technique is using the specialized software on the computer of the testing machine, in order to establish the crack length propagation, by collecting the data from the machine loading cell, and also from the clip-on-gage extensometer that is attached on the compact specimen. For the second method, the experimental data on the crack length propagation are supplied by a dedicated crack propagation gage, provided by Vishay (Tk-09-CPB02-005/DP) and bonded in the vicinity of the initial small crack, initiated by fatigue. Finally, a comparison of the results obtained with the two methods is made; one can say that the advantage of the second method consists in its amenability for studying the crack growth rate on a real component, even without interrupting its working process.