vintage casio bm-100wj altimeter barometer depthmeter watch rare from 1989  

Generally speaking, when the atmospheric air pressure increases the weather improves, and when it decreases the weather deteriorates. The BM-100WJ was a digital watch with a weather-prediction function based on this principle. The watch had an internal semiconductor barometer sensor that measured the air pressure every three hours, and showed the data on a bar graph display. When the bar on the right hand side went up, it meant the weather would improve, and when it went down, the weather would get worse. This air pressure data could also be used to tell the wearer his or her approximate altitude or underwater depth. These revolutionary new functions made the BM-100WJ a major hit product. Casio went on to create a whole line of sensor watches with various functions,