??

Two question marks, ??, indicate a serious error, commonly called a blunder. The move damages the position drastically, for example by losing a valuable piece, allowing checkmate, an attack on the king with no legal defense, or turning a winning position into a loss.

Not every ?? has an immediate consequence. Sometimes the damage becomes clear only after an exact sequence. Severity also depends on context: the same oversight can be decisive in one position and less important in a position that was already lost.

? conventionally marks a less severe error. !! sits at the opposite end and gives strong praise. A program may read ?? in Portable Game Notation (PGN), the plain-text game format. When saving the file in standard form, it replaces ?? with $4, a dollar sign followed by the number 4.