K&E bamboo slide rule.
I started school before the pocket calculator… for me, the first I could afford was the Texas Instruments SR-50 calculator (I could not afford HP35 calculator). My physics labs took 12 hours of work… 11 of the hours futzing with the slide rule. When I got my SR-50… the time to complete a lab went down to one hour! Speaking of a time saver.
It was with great pleasure decades later I ended up working for Texas Instruments.