A piece appears in a position. Defended or hanging? You have a second to decide, and a minute to decide it as many times as you can. Hanging? trains the single most valuable reflex in club chess: the attacker/defender count, compressed to a glance. More rating points are lost to free pieces than to any opening mistake — at 800–1400, games are won by the player who stops donating material first. After a few weeks of rounds, the check runs before every move automatically: yours, and your opponent's. The anti-blunder drill.