To be honest somefolk get on better with a whizz wheel than a calculator.
Better tell me which airline they work for so I can avoid flying with it? Air France perhaps?
I've been an "engineer" all my life, and used the slide rule at school in the late 1960s so I am fully familiar with how it works. But that's where it belongs. No "engineer" I know uses one today. It's a multiplication/division device; that's all. The wind side of the aviation slide rules just does a geometric solution to the wind triangle, but you don't need to do that unless dead reckoning, which nobody does when flying somewhere "for real" today.
The reason we still have this antiquated device in the syllabus and in the exams is because the JAA material was finalised c. 1998, and was written by ex national Air Force navigators (and similar types) who were retired even before that date. Practically everybody who has been involved with
today's ATPL exams had finished with aviation in all practical sense even before GPS came along in the late 1980s.