Your decision quality graded against the coach’s EV math — each trainer decision is scored on how close it came to the highest-EV play, then blended into one number. It measures whether you chose well, independent of whether the cards fell your way.
Sharpness is luck-free: a correct call that lost still scores well, a lucky bad call still scores poorly. That is the point — results over a short run are mostly variance, but your decision quality is measurable immediately. Watch it by street to find where your game leaks: many players are sharp preflop and on the flop but bleed EV on turns and rivers.