I went to college in the early 70's. Electrical Engineering major, and calculus was my hardest class. Regular math, algebra, trig, geometry came easy, don't know why I had such a mental block for calculus, ended up never having to use it my whole career. Those days we used slide rules but electronic calculators came out during my college days, most professors wouldn't let you use them in class.
On another note my physics professor had worked at Los Alamos on the A-bomb. He was a weird duck, almost blind he had to use glasses that looked like binocular eyepieces. He could fill up a chalkboard with formulas and theories non-stop. He was so smart that he was very hard to follow, at least for the dumdums like me.
