Answer:

In standard, trending impulsions, the time of wave-2 must equal or exceed that of wave-1. In addition, wave-4 must also equal or exceed the time of wave-3. Since it appears a 5th extension, standard impulsion began at the low in 1982, I simply measured the time of wave-3 (which was 18 years - from 1982 to 2000) and assumed wave-4 would take that much time or more.

Under different wave structure circumstances, wave-4 might take far more time than wave-3, but with wave-2 already much smaller (just 7 years), the rule of alternation had to be taken into account along with the concepts of degree and similarity. To avoid wave-4 being too larger in relation to wave-2 (in time), I opted for the shortest allowed time-frame for wave-4 (i.e., 18-years, and just rounded up to an even 2 decades).