Before the Hamilton Pulsar (once thought to be the first calculator watch), a gift giving advertisement in the June 1975 issue of Playboy magazine included the Calcron LED Wrist Calculator (pictured left). One of the most collectible, only 50,000 of Hewlett Packard's 1977 HP-100 (pictured center) were made, of which about half were purchased by a Saudi prince. That same year, Sinclair introduced their DIY kit that didn't include a watch function (pictured right) and between 1976-78 Hughes Aircraft Company produced a similarly bulky piece that made appearances on Battlestar Gallactica. Since then, the 80's brought LCDs and every imaginable company produced LCD calculator watches. Go here for more details and images.