A pinball machine is an arcade game that normally consists of a large glass-covered table with three miniature playfields. The player uses large metal pins or flippers to push the ball onto one of the fields and try to achieve goals, such as getting all the balls onto one field or completing a certain number of pulses with special balls. Each field may include holes that can be used to jump other balls into them and so beat them out. A ground pinball machine may also have a working clock so balls can be set to strike at predetermined times. The player attempts to achieve goals by moving the ball around the playfields and firing it into holes. The game starts when the player pulls a handle located in the coin box, which raises a steel-frame gate that covers one of the playfields. The player may then play without shooting anything until they have won enough points through normal field manipulation to open the gate fully and win games. The ball is usually made of clear plastic, controlled by one to three flippers on the left, right, and bottom sides. The power of the flipper and placement of the flippers may be adjusted by the operator to make the game easier or harder for different players. Although most machines are designed to play with two balls simultaneously, some software has been written to allow four balls (or even eight) to play on a single machine.