>one was circular so it would be more accurate :-)
I have never used a slide rule, and I am missing the joke. Is that true? My assumption would be that humans are better manipulating a linear device than angles.
The longer a slide rule the more precise it is - you get mode decimal places. But it also become less convenient to use. That's where the circular slide rule comes in: a 4 inch diameter circular slide rule has the scales on its rim, which are 4 * 3.14 = 12.56 inches long, so it's equivalent to a 12.5 inch linear slide rule but more compact. That's how a Breitling wristwatch can include a usable slide rule - it's equivalent to a 6 inch linear slide rule on your wrist.
Also, in a linear slide rule you have to move the center scale left or right: to multiply 2 * 4 you move the slide to the right, but to multiply 3 * 4 you need to move it to the left (it "overflows"). With a circular slide rule you don't have that problem.
To build on the other answer. Precision is the word you want, not accuracy. My mother had an extra-long slide rule which sadly disappeared in some cleaning/move. But a circular slide rule can mimic linear length to some degree while staying fairly compact.
I have not used either but I assume it is possible due to it being easier to manufacture a pivot point with tight tolerances so there isn’t much play in the slide.
It's not really an accuracy problem AFAIK. But the precision (i.e. number of significant digits) is limited by the effective length of the scale (whether linear or circular) even if the manufacturing accuracy is perfect.
Also, in a linear slide rule you have to move the center scale left or right: to multiply 2 * 4 you move the slide to the right, but to multiply 3 * 4 you need to move it to the left (it "overflows"). With a circular slide rule you don't have that problem.