The word “obsolete” is NOT the same as the word “old”. Neither a 1970s TI calculator nor a slide rule is obsolete.
Having used a “sly drool” thru college and later - and having adopted the use of an HP-35 to do homework in preparation for the Professional Engineer exam, I forgot one day to bring the ’35 home from work. No problem, right? I just broke out the old slide rue and tried to do the homework.I can assure you that a slide rule is well and truly obsolete.
If you’re out of practice - and perhaps even if not - keeping track of the decimal point is simply too hard.