I was under the impression that you could measure your barrell roll or boost. In fact, you aren't committed to that action until you've actually moved your piece.
Wrong. The moment you declare for example a boost to the left, you must perform that boost if you can. And you can't pre measure it. That's why when i teach newbyes, i don't let them pre-measure, they get bad habits.
What about a player placing the template down for a boost/barrel roll that he knows will bump and be denied? He has the right to do so, RAW, but it does allow him to see the template on the table for comparison's sake. Is that against RAI?