Language matters. So, I thought it might be a good idea to fix the meaning of some words which pop up often on this Web site. Don't worry; there aren't many and most seem pretty reasonable. Still, in any axiomatic system it makes sense to nail down the definitions one starts with. Here we go.
Slide: No mystery here. This is the part of the rule which slides left and right.
Stator: Sometimes called the base, this is the fixed part of the rule within which the slide, well, slides.
Cursor: This is the clear window which slips over the rule allowing you to see how a reading on one scale aligns with a number on another scale. The hairline associates the two.
Mantissa: On a slide rule this term assumes a slightly different meaning than it does in the realm of computation with tables of common logarithms (like I labored under when first taking college trigonometry). This corresponds with how we might write a number in standard scientific notation, e.g., 2.345 * 10^3. In this case, we'll call the 2.345 the mantissa.
If you're curious, with common logarithms, one would treat it as 0.2345 * 10^4 and refer to the 0.2345 as the mantissa; the 4 of 10^4 is called the characteristic, incidentally.
Some people refer to the slide rule or scientific notation version as the significand just to distinguish it from the mantissa of common logs.
Anyway, look at the C scale, for instance. In all of our work with the slide rule here, we'll call the mantissa a number which ranges from 1.0 on up to 10.0 on the scale.
Left Index: Refer to the C scale again. It commences with 1.0 and we'll call this the left index.
Right Index: Again, refer to the C scale. It concludes with 10.0 and we'll call this the right index. Note that this can also be considered a 1.0 within the next order of magnitude.
Index-Swap: Say you've got the left index of C aligned with 5 on the D scale and now need to locate 7 on the C scale. Unfortunately, it's off-scale, way to the right. So, we bring the right index back to replace the position of the left index and proceed. This is an index-swap and while mathematically legitimate, should be avoided whenever possible since it introduces a certain amount of operator imprecision or inefficiency.
Scale-Transfer: Here you're doing a computation on two scales and for various reasons need to transfer intermediate results to a different pair of scales. Hence the value of the hairline in the cursor. This operation is frequently required when working with the folded scales CF and DF, or the ST scale (which is itself a folded scale when you stop to think about it).
Duplex-Flip: In this case, you turn a duplex style rule over, leaving the cursor and slide in place. It's a grand scale-transfer, if you will, correlating all of the scales on the obverse side with all on the reverse side. Of course, this presupposes you've calibrated the two opposing hairlines in the cursor!
Equals: Now here's a curious word to think requires a definition! Equals is equals, right? Well, the slide rule is an analog device, and given the continuous nature of both the real numbers and a stick purporting to represent logarithms of those real numbers, it seems prudent to say a few words. In particular, throughout this Web site, when I mention a result is equal to something, take it to mean that the result approximates the true value to two or three decimal places. Moreover, it's often convenient to ignore the order of magnitude when making such statements. So for example, "the square root of 2400 is 4.9." It's always assumed you'll adjust the order of magnitude at the conclusion.
Next installment: Slide Rule Resources