For two on one device: whoever leaves the main line first loses the round.
Round 1
Two players, one device. At the top stands a main line, for example Ruy Lopez: Closed, main line. You play it alternately move by move on the board, one with White, one with Black.
Whoever leaves the book first loses the round. The other gets one point for every move they played correctly, plus 5 for the win. If you both know the whole variation, each gets 5 points. After every round the colours change.