Wearable computing, although widely believed to be the latest technological innovation, had existed even during the days of the abacus, a calculating tool that was used centuries ago by merchants and traders. According to a historical source on Chinese culture, it is believed that an abacus inlaid in a ring was used as a calculator during the Qing dynasty (http://www.chinaculture.org/classics/2010-04/20/content_383263_4.htm):

A relatively recent modern form of wearable computing devices is the Casio Databank. It's a series of electronic wristwatches manufactured by Casio during the early 1980s that were bundled with features such as a calculator, timer, world clock, contact management, and also a remote control for TV and VCR.

It was very popular and was considered a technological marvel of that time. It was very convenient compared to the manual or simple digital watches that were available during that time. It was not only used for checking the time and setting up alarms but also helped with utility functions such as calculating something fast on the fly or for recalling stored contact information:

Innovators and inventors have always been fascinated with bringing technology and lifestyle as close together as possible. Whether it's the Burton Amp jacket, which is believed to the first known modern wearable device for controlling iPods, or the latest wearable device called Whistle that is used by pet owners for tracking their pet's location and activity, wearable devices are becoming commonplaces.