Even the cheapest and least complicated digitals (电子表,电子钟) are minor miracles of modern technology. They replace the traditional hands, springs and cogs with flickering digits and electric circuits. Some just display hours, minutes and seconds, but many function like baby computers. At the push of the button you can check the time in New York or New Dehli, see exactly how long Mario Andretti takes to lap a race track, set a small but shrill alarm, or even program the watch, months in advance, to flash out a reminder about birthdays and other special dates. Some digitals have calendars that "know" all about leap years and will remain accurate well into the next century. Quartz (石英), one of the world's most common minerals, lies at the heart of every digital watch. Almost a century ago, scientists discovered that quartz crystals vibrate at an absolutely constant frequency when an electric current is passed through them. But quartz digital watches didn't become practical until miracles of miniaturization (微型化) were developed to save weight and room in spacecraft. The typical watch crystal, powered by a battery the size of a fingernail, vibrates 32,768 times every second. The vibrations are fed into a tiny "chip" — little bigger than the end of a match — which is crammed (塞入) with more than a thousand transistors and other components. This microscopic maze is the watch's "brain" and can be designed to store a remarkable amount of information. But its most important single function is to keep dividing the vibrations by two until the quartz is pulsing precisely once every second. Battery, crystal and chip combine to produce remarkable accurate watches whose timekeeping rarely strays by more than one or two seconds each month. They are also reliable. If you fancy a digital watch, ask yourself how many of the tricks it performs are likely to be of genuine value. It makes no sense to spend extra money on what could become useless once the novelty has worn off.