I never spent the time to get quick with it, but I could absolutely see it being quicker than a calculator. You’d just have to be aware of the limits to its precision if you were in a field that required it.
One problem with a slide rule is that it only performs operations on normalized mantissas. You have to keep a parallel exponent calculation in your head, and that slows you down. Also, maintaining best precision slows you down.
For multiplication, the DLDP in the result is:
- the sum of the DLDPs of the multiplicands MINUS 1 if the multiplication is done with the slide sticking out to the right of the ruler's body (for example 2.0 x 3.0 = 6.0).
- the sum of the DLDPs of the multiplicands if the multiplication is done with the slide sticking out to the left of the ruler's body (for example 5.0 x 4.0 = 20.0).
There's a similar rule for division, but that's left as an exercise for the student.
We were taught to estimate and use the rule to refine. I date back to the early electronic calculator era and we still had textbooks referencing slide rules etc.
"I want a dropping resistor for a plain old 1980s LED in a car" (back in ye old red LED 20 mA days) "Well experience indicates that will be far more than 500 ohms and somewhat less than 1K and IRL you're probably going to install a 680 and call it good" If you want an actual calculation for engineering purposes you calculate the ideal value under worst case conditions as about 585-ish ohms or whatever using the slide rule, purchasing LOLs at the idea of buying 0.1% precision resistors for mere LEDs, installs cheap 680 ohms and ships it. Maybe 680s if you want it bright to see in daylight or 820 if you want better odds to survive an alternator field winding dump or open battery (about the same thing). You can at least use the slide rule to verify everyone rounded in the "safer" direction to handle the worst case scenario.
I did keep a slide rule as a backup for exams in college when calculators were still LED but never really used one after a couple of years in high school.
They do what people want, the keyboard feel is infinitely smoother than tapping on a phone, etc.
Yeah, the 12C was the standard in business school. But I needed a new calculator and the 41 with its various modules worked fine and was more general purpose.
We have speed electronic calculators now instead of slide rules, but they give a wronger answer and people aren't even aware of it or know why.