Ah - I never could get the hang of slide rules in high school. Consequently, (and since I also could not do math in my head), I failed Chemistry. I understood the subject, but since so much of the grade was based on daily pop quizzes that involved intense calculations, I could never complete them in time.
The happy end to that story is that I retook Chem in summer school, and at that school they had electric calculators that we could use. I got an "A" and was at the head of the class.
This was the first glimmer of the revolution that would allow me to have a tech career. Calculators and personal computers made actual arithmetic skill unnecessary. As long as I could ask the right questions and form the right logic, I could get machines to do the actual number crunching.
I was born at just the right time!