<Li> Double check . A double check is a check from two pieces to the opponent's king in a single move . This happens when a moved piece attacks the king, resulting in a second piece giving check by discovered check . It can also happen, though very rarely, when an en passant capture opens two lines of attack simultaneously . In algebraic chess notation, a double check move is sometimes noted with a "+ +" after the written move in place of the usual "+", although "+ +" has been used to indicate checkmate (along with "#"). A double check cannot be blocked, nor can it be met by capturing one of the checking pieces (unless the king itself makes the capture), because there is check from two directions . </Li> <Li> Cross-check . When a check is answered by a check, particularly when this second check is delivered by a piece blocking the first, it is called a cross-check . In fact, a "cross-checkmate" is also possible in that way (that is, to answer a check with a checkmate) but since no such term exists, it would be called cross-check as well . Cross-checks are rather rare but are a popular theme in chess problems . </Li> <P> In friendly games, the checking player customarily says "check" when making a checking move . Announcing "check" is not required under the rules of chess and it is usually not done in formal games . Until the early 20th century a player was expected to announce "check", and some sources of rules even required it (Hooper & Whyld 1992: 74). </P> <P> In algebraic chess notation, a checking move is recorded like any other move, except that a "+" is normally written after the move . </P>

When do you have to say check in chess