Generally, slide rules were only good for rough calculations (3 significant digits if you were lucky), but they did contain multiple scales providing multiplication, division, exponential, log10, ln, roots, sin, cos, tan, and hyperbolic trig functions. Notably one couldn’t do addition or subtraction with a slide rule; we used pencils for that.
When more precision was needed, I and my fellow engineers would break out our copies of CRC’s reference tables. The better log tables allowed calculations to 5 or 6 significant digits. Using these were not unusual and all of us learned to use them in high school (before 1970 at least).
Back in the 1970s I used a slide rule when 2-3 place accuracy was enough; or 5-place or 7-place log tables and a pocket mechanical adding machine (rather than by hand) when more accuracy was required.
I found a 2-minute video of the sort of pocket adding machine I used,
https://www.youtube.com/watch?v=ryST18JJ7VU
(The device is actually easier to use than shown. Using the colors next to the digits: if silver, pull the stylus down; if red, pull up and over the curve at the top of the column to the next digit. No extra or wasted motions are needed.)
Five places were usually enough, but seven places were needed for some astronomical calculations such as eclipses. The $7 I paid for the log tables in the late 1960s would purchase about $50 today; and the adding machine was probably a couple of dollars back then.
Of course you are right, the slide rule works with logarithmic scales that are “added” together to do multiplication. Linear scales could be used to add, but the low number of significant digits (no more than three on standard slide rules) meant that it wasn’t worth it, and no engineering slide rule that I ever saw had scales for addition.
When more precision was needed, I and my fellow engineers would break out our copies of CRC’s reference tables. The better log tables allowed calculations to 5 or 6 significant digits. Using these were not unusual and all of us learned to use them in high school (before 1970 at least).