Restaurant diners view reservations as solid contracts when they show up on time, open-ended agreements when they show up late, at-will arrangements when they show up unannounced and tentative suggestions when they do not show up at all. The public could benefit from a refresher course in Reservations 101.

A reservation is an appointment whereby a person promises that a party will arrive at a specific time. An accepted reservation is a probability, not a guarantee.

A restaurant's success depends on its management's ability to meet sales projections. Projected sales are the function of two numbers, one a constant (average check price) and the other a variable (covers, or diners). A restaurant's budget, how much labor it employs and how much inventory it carries, is based entirely on its projected revenue: (average check x covers). Restaurateurs accept reservations to take some of the guesswork out of calculating the number of guests they will serve.

Unpredictable changes in reservations hurt a restaurant's fiscal health and punish other diners. Items:

* No-Shows: People who fail to cancel reservations renege on a promise to help a restaurateur and his staff, in effect, pay their rents. They do not care that the restaurateur has turned away other business and had to wait at least 15 minutes before seating a walk-in party in their place. Not to mention that they reduced the income of the person who was going to serve them.

* Overbooking: "Oh, restaurants always overbook," is the reply thoughtless people offer to the question, "Don't you think we should cancel our reservations?" Overbooking is not an offensive ploy; it is a defensive strategy to avert the threat of economic disaster posed by no-shows.

Many restaurants have instituted the terrible policy of guaranteeing reservations to a credit card and charging no-shows a fee. It is not enforceable; if a diner contests the charge, the credit card company will issue a "charge-back" to the restaurant and then demand proof -- which does not exist -- for a purchase that did not take place. Moreover, whatever paltry fee the restaurateur could charge is not worth the bad faith its collection would inspire. The policy offends everyone, but the people who object the loudest are those who abuse the reservation system the most.

* Late Arrivals: Late parties have turned themselves into walk-ins. They throw everything off-kilter for everyone else. A restaurateur generally allows 11/2 hours for a lunch reservation and 21/2 hours for dinner. Vacationers with a Saturday-to-Saturday time-share condo understand they must still depart on Saturday even when they didn't arrive until Monday, yet the 7 o'clock reservation that "ran behind" by 30 minutes feels no urgency to vacate the table for the 9:30 party that was punctual. The restaurateur then gets to buy two rounds of drinks: one to buy the patience of the innocent party, the other to buy back the table of the guilty diners.

* Incomplete Parties: They're late. See above.

* Walk-Ins: People who announce upon arrival that the size of their party has changed also have transformed themselves into walk-ins. It is a big deal when a party of six becomes a party of two. Perhaps the restaurant has turned away other parties of six. The host has to scramble to find a deuce that does not exist. The server who was to have waited on the party of six might have lost 20 percent of his income for the evening. Adding a fifth chair to a table set up for four can compromise the comfort of diners at adjacent tables.

* Squatters: Like the hairdresser's chair and the doctor's exam room, a restaurant table is time-shared, not purchased, space. When the hairdo is done and the physical is over, clients and patients do not "hang out" ad infinitum. When the coffee cups have been thrice emptied and the check presenter has acquired a layer of dust, the diner's lease has expired and it is time to go.

-- David Hagedorn