A record on the left, the same record rewritten for the patient on the right, and a ribbon between every pair. Thickness is how far the meaning moved. Colour is which way it went.
Drift here is not word difference. Two sentences can share almost no vocabulary and carry the same instruction, which is a good rewrite. Drift is how much of the action moved: the dose, the threshold, the trigger, the thing the reader is supposed to do and when.
Pull the threshold up and the thin teal ribbons go dark. What remains is the shape of the problem: a small number of links carrying almost all of the clinical risk, sitting in a letter that reads perfectly well. The last row is the one worth staring at. A prohibition became a permission, and the sentence got shorter and friendlier while it happened.
This is a measurement a reader can see rather than a score they have to trust, which is the point of building it as a picture and not a table.