SAN JOSE, Calif. (AP) _ If it lasted 1.6 million years, Hewlett Packard Co.'s newest clock would be off by just one second, making it the world's most accurate mass-produced timepiece. But it won't likely show up on any home mantels.

At $54,000 each, only scientists, navigators and some governments that set time standards are expected to buy the atomic clock, HP 5071A, that's scheduled to be introduced Tuesday. It's called an atomic clock because it relies on the vibrations of cesium atoms instead of springs, pendulums or electric motors.

''We were wondering if it might show up in the Neiman-Marcus catalogue, but we haven't heard of any individuals wanting to buy such an accurate clock,'' said Len Cutler, who worked on the newest clock and on the first one HP introduced to the world in 1964.

''It shows time, of course, but it's used for its timing accuracy, not really for what it says on the outside.''

Still, one of HP's older atomic clocks displays the time in the airport at Geneva, considered by many the world's time-keeping center because of its tradition of watch-making.

The new clock looks like a VCR - 22 inches deep, 19 inches wide and 5 high. It is more than five times as stable as the old model and comes with a remote control. It has a digital readout showing the hour, minute and seconds.

The more accurate the timepiece, the more accurate the navigation of everything from the space shuttle to troops and weapons to ships at sea.

The clock emits an electronic signal once every second, allowing users to synchronize machines for time keeping, navigation, astronomy, electronics, radio and television signals, telephones and computers.

The precisely timed pulses also allow equipment like telephones to handle more information.

''In digital communications, the more accurately the pulses are timed together, the more information you can pack into a frequency band,'' explained HP communications manager Al Thorne. ''And everything from telephones to computer networks are going digital these days.''

HP's atomic clock achieves its high accuracy by synchronizing a microwave signal with the vibrations of atoms of cesium 133, the accepted worldwide definition of time.

Some of the world's standard time keepers use HP atomic clocks, including the U.S. Naval Observatory in Washington, the National Institute of Standards and Technology, the Observatoire de Paris, the National Physical Laboratory in England and the Physikalisch-Technische Bundesanstalt in Germany, according to HP.

But even HP's new atomic clock isn't failsafe. The company predicts one failure every 10 years or so and provides only a 5-year limited warranty.

''I don't think anyone expects a product to last 1.6 million years,'' Thorne said.