Manual player substitution double

The board the fourth official raises at the touchline to show a substitution. It is double faced with two digits: the number of the player coming on is shown on the IN side and the number going off on the OUT side, so both benches and the stand read the change at once.

The board is set by hand and needs no power, which makes it the practical choice for a pitch without an electronic scoreboard, and the fallback for one that has.