My guesstimate 50e3 out of the world’s population of 6,505,523,636 or 7.68e-10% of the worlds population, based on extrapolation of known data on one pipe stress program...
My experience has 9 out of 10 people not being trustworthy of doing the work unsupervised but perhaps I'm too harsh!
Overall a very small group….
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Best Regards,
John C. Luf