SEIKO 5 - the meaning of the "5" A great marketer had the idea in the 70ies: to be a SEIKO 5, the watch has to have the following 5 (five) attributes (thus the name SEIKO 5): 1. Automatic, 2. Water resistant, 3. Shock resistant, 4. Date, 5. Day. Please note that some SEIKO 5's are in fact SEIKO 4's, if the "Day" function is omitted, then the Caliber 7S25 is used. The only difference to the normally found 7S26 is the omission of the day wheel. Also re-issues of SEIKO 5 Sports often use the 7S36 caliber. Again the 7S36 is similar to the most popular 7S26, yet it features 23 Jewels as opposed to the 21 Jewels in the 7S26. Please note that all these movements beat at a rate of 21'600 bph (beats per hour) or 6 bps (beats per second). As a comparison, an ETA 2824-2 beats at 28'800 bph or 8 bps. A Miyota 82xx beats at 21'600 bph. Why do I mention these three movements? Because they are found in probably 80% of all inexpensive automatic wrist watches. A market share that is huge, yet challenged these days (2006) by an increasing share of inexpensive China Made automatic movements An automatic watch (also called a self-winding watch) is a mechanical watch, typically with a balance wheel escapement, whose mainspring is wound by the motion of the wearer's arm, instead of having to be wound manually every day. Whereas a quartz watch is powered by electricity, a mechanical watch is powered by a mainspring which must be rewound for the watch to keep time.