Coverage shows you a position and asks one question, over and over, against a sixty-second clock: which squares are attacked, and which are safe? It sounds basic. It is the most important sight in chess. Every blunder that makes you groan — the bishop dropped to a pawn, the queen trapped on a square the knight covered — is a coverage mistake. Masters don't calculate whether a square is safe; they see it. Coverage builds that sight with pure repetition: read the position, mark the squares, get faster, get right. One minute per round. Your accuracy and speed feed your Mainline weakness profile, so if coverage is what's costing you rating points, your daily queue will tell you. Train it until "I didn't see that" stops being something you say.