A hand pay could also be necessary as a result of a short pay. Hopper fill slip is a document used to record the replenishment of the coin in the coin hopper after it becomes depleted as a result of making payouts to players. The slip indicates the amount of coin placed into the hoppers, as well as the signatures of the employees involved in the transaction, the slot machine number and the location and the date. MEAL book (Machine entry authorization log) is a log of the employee's entries into the machine. Low-level or slant-top slot machines include a stool so the player may sit down. Stand-up or upright slot machines are played while standing. Optimal play is a payback percentage based on a gambler using the optimal strategy in a skill-based slot machine game. Payline is a line that crosses through one symbol on each reel, along which a winning combination is evaluated. Classic spinning reel machines usually have up to nine paylines, while video slot machines may have as many as one hundred. Paylines could be of various shapes (horizontal, vertical, oblique, triangular, zigzag, etc.) Persistent state refers to passive features on some slot machines, some of which able to trigger bonus payouts or other special features if certain conditions are met over time by players on that machine. Roll-up is the process of dramatizing a win by playing sounds while the meters count up to the amount that has been won. Short pay refers to a partial payout made by a slot machine, which is less than the amount due to the player. This occurs if the coin hopper has been depleted as a result of making earlier payouts to players. The remaining amount due to the player is either paid as a hand pay or an attendant will come and refill the machine. A scatter is a pay combination based on occurrences of a designated symbol landing anywhere on the reels, rather than falling in sequence on the same payline. A scatter pay usually requires a minimum of three symbols to land, and the machine may offer increased prizes or jackpots depending on the number that land. Scatters are frequently used to trigger bonus games, such as free spins (with the number of spins multiplying based on the number of scatter symbols that land). The scatter symbol usually cannot be matched using wilds, and some