The R1 and R2 scales are for finding squares and square roots, when used in conjunction with D.
In this respect they are like the A scale, but they offer higher precision.
On a given slide rule, they either appear together or not at all.
read the tutorial on squaring, cubing, and roots
- The R scales are a C scale stretched to double its length, and cut in half. The first half ( from 1 to 3.1 ) is called R1, and the second half ( 3.1 to 10 ) is called R2. You use R1 to find square roots of numbers with even scientific notation exponents, and R2 to find square roots of numbers with odd scientific notation exponents. As well, numbers on the R1,R2 scales find their squares on the D scale.
- It's confusing that R1 is for even exponents and R2 is for odd. It's even more confusing that Q1,Q2,and Q3 have similar rules where you must subtract 0,1,or 2. The reason is that R1,R2 are the traditional names, and instructions for using them were based on a concept of "the number of digits". Griffenfly instructions are all based on scientific notation, and the exponent in scientific notation is one less than the "number of digits". We could have reversed the scale names, but that would be very confusing to people familiar with R1 and R2 on other slide rules.
In the case of Q1,Q2,Q3, we could definately have changed the names, since other slide rules don't call them Q at all, but print a little cube root symbol instead. But for consistency with R1,R2, we also start them on 1.
- A is made from compressing a D scale, whereas R is made from stretching it. R is 4 times longer than A. You lose some precision using A, and you gain some using with R1,R2. At max zoom on R1, you can often read values to 6 decimal places and estimate a 7th, meaning less accumulated error in long calculations. You can't read 7 digits on A.
The drawback to using R is that it takes up two scale positions, and A only takes one. (But of course most people build a slide rule with an A,B combination anyway, so the drawback is minimal)