Well, not exactly.....
In the case of drilling 2 holes, let's say that they line described by the center of each holes lies at 20° from the hard jaw of your vise, for example......
If you are using Cartesian coordinates, the first hole wold be considered the origin, in all likelihood, even if it were an inch off the hard jaw and half an inch from the edge of the material. It's simpler to explain if we set our X and Y zeroes at the first hole. Let's say that your hard jaw represents the base of that triangle, end hence the "c" figure. We've determined that the length of side "c" is immaterial. It's just a reference line (or plane if you want to think about all this in 3D, and it gets a bit hairy then). So you can move along the X axis any desired distance. But as of yet you don't know that distance. But you know the desired angle to be 20°. IF you wanted the holes spaced 2.500" apart c-c, then we can see how this works like the sine bar. Your DRO won't tell you the length of an angular move, directly. But we know it will be less than 2.500" because of the arc swept by what now pretty much amounts to a piece of a bolt circle. We know the -Y- move, however, to be 0.8551. So now we have information to use another section of your chart. We know side "a"(0.8551), we know angle "A" (20°), and we know side "c", (2.500)
So our second hole will be at -Y-0.8551 x -X-2.3492
cosine A * c = side B, which is the -X- axis move.