Chess notation cheat-sheet (for new readers)
Pieces: K king · Q queen · R rook · B bishop · N knight · (a pawn move has no letter)
Actions: x takes · + check · # mate · O-O short castles · O-O-O long castles · e8=Q pawn promotes to queen
Annotations: ! good move · !! brilliant · ? mistake · ?? blunder
One move, two attacks
A discovery works because a single move splits in two. The piece that moves makes its own threat, and as it clears the line it unmasks a long-range piece parked behind it: a rook, a bishop, or the queen. Now two things are hit on the same turn, and the defender gets one reply to deal with both. Stopping one leaves the other standing, so material comes off the board.
Most players spot the loud half and miss the quiet half. Say both out loud before you commit: what the moving piece does, and what the line behind it now reaches. The biggest payoffs come when the front piece can grab a rook or queen while the rear piece ties down the defender. These puzzles pull from positions where exactly that double threat decides the game, so you drill the full move and not just the capture you would have played anyway.
Discovered check and double check
Discovered check. When the line that opens up hits the enemy king, the discovery becomes a check. That changes everything, because a check has to be answered before anything else. The front piece is suddenly free to take a queen, a rook, or whatever sits in its path, and the opponent usually cannot save the captured piece until the check is dealt with.
Double check. Here the moving piece gives check and the piece it uncovers gives check, both at once. The king cannot block two lines, and it cannot capture two attackers in one move. It has to step away, full stop. That forced king move is why so many mating nets run through a double check, and why it is the sharpest version of the idea. The puzzle set keeps both types in rotation so you learn to tell which one a position is offering.
Spotting discoveries in your games
Recognition comes from a habit, not from harder staring. Each move, scan for two of your own pieces stacked on one line: a rook or queen down a file or rank, a bishop on a diagonal, with another of your pieces sitting in front. That setup is a battery, and the front piece is the trigger waiting to fire.
Then ask what the front piece can do once it leaves. Aim the rear piece at the king or the queen and the value of the discovery jumps, since a check or a hit on the queen forces a reply and buys the front piece a free turn. One more cue worth trusting: when a piece of yours looks oddly placed, blocking its own rook or bishop, read that as loaded rather than clumsy. I lose this most in blitz, grabbing the obvious capture before noticing a rook was about to wake up behind it. The trainer leans on this. Set the rating slider where you solve around 75 to 80 percent, the range where these shapes actually stick, and the three free hints will flag the opening line, then the hidden piece, then the move, when a position stalls.