There are many Law Courts around Athens. Athenians like to come and see the heated arguments that take place there. Hundreds, even thousands, of people pack in to the buildings to take part in the jury.
Those people on jury duty in a particular year are given a bronze token (called a pinakion) on which is inscribed their name and a letter, from alpha to kappa. A special machine called a kleroterion is used to select those who will sit on a jury from those available for jury duty. When a jury is needed, those people on jury duty come together and place their token in one of ten baskets, each of which has a letter on it from alpha to kappa. The people place their token in the basket with the same letter as their token. The tokens from each basket are placed in the corresponding column, from alpha to kappa, of the kleroterion.
A number of black and white balls are mixed up in a basket and then poured into a funnel in the side of the kleroterion. A crank at the bottom of the funnel is turned to release one of the balls. If it is a black ball, then the first row of tokens in the kleroterion are discarded - these people won't be jurors today. If it is a white ball, the people whose tokens are in the next row of the kleroterion are selected as jurors. The crank is turned and a ball released for each row of tokens in the kleroterion in turn. Those people selected as jurors would now have to attend a trial.