Here ir the text including this termin:

Fig 8 shows a schematic view of a possible development of hydrogen content/concentration 46 in oil over time in the tap changer where each tap change is associated with a up-tic of the concentration of hydrogen. This is to illustrate that the analysis system also have to include the frequency of tap changes or the time between taps. A large number of tap changes 51 might generate a larger increase of hydrogen than on with much fewer taps 50. But the increase of the curve 50 with few taps might indicate a problem. The system has to be able to, and is suitably adapted to, separate the two cases 50, 51 and might give a warning/alarm for 50 but not for 51. The relative size of the curves and alarm levels in figures 6-8 are only for illustration.