Sourdough baking
They mean 30 degrees from horizonal, or compared to the cutting surface. You want to hold the lame parallel to the surface and then lift the edge that's further from the loaf by about 30 degrees.
It also helps to start the cut with the corner of the lame. I personally got better ears by going in a second time to reinforce the same cuts.
Cool! Thank you! And how far up the loaf do you cut it?
This is kind of subjective... what kind of loaf are you trying to make? There's a million different viable scoring patterns depending on the shape. If you're trying to make a traditional demibaguette you'd want to have maybe 3 diagonal cuts overlapping each other by about a third going down the loaf, but there's really no hard and fast rules there.
Fair enough!
The bread code went into a lot of detail about this. Think he's got a diagram out there too explaining it! So, give this a try - if your loaf is a batard shape - score it on the side (not on the top surface). And hold the blade fairly close to fully horizontal with your table (which means it will be at about the correct angle with the bread).
And if it’s just the angle of the blade, how far up the side of the dough do you slice it?