If it’s really shifty, sail upwind and focus on learning the maximums and minimums (high and low headings) on each tack, and whether there’s a pattern to the shifts. Sail through a whole phase on one tack, from all the way headed to all the way lifted. When I sailed collegiately on upstate New York’s Lake Seneca, we would have races with 40-degree shifts. On one tack you’d be sailing toward the mark, and on the other you’d be sailing away from it. In such shifty conditions you’re better off spending your warm-up time on learning shifts than on boatspeed. Conversely, if the conditions are such that one side is usually favored, and there might be just a small shift or little bit of a pressure difference, 90 percent of that race, assuming you’ve had a good start, will be boatspeed related.