^^^ Punch cards ... there's nothing like a huge 370 Assembler program in a deck of cards ... just don't drop them
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I was very adept at doing hexadecimal arithmetic in my head .... for a byte or two. The best calculators ever .... those that did hex conversions/math!
And Boolean Algebra .... the basis of any "logic class"... my prof wanted me to tutor others ... sorry... you either get "it" or you don't imo.