Introduction
Small smart watches are gaining popularity as the leading wearable computing device. Smart watches make interaction for frequently used smart phone functions (e.g., checking for time, message, incoming calls, body signals, etc.) convenient through its wearability and mobility (e.g. light, small, fashionable and ergonomically located on the wrist). It can also be effectively be used as an auxiliary input device for glass based mobile augmented reality (AR) [ONT*15, PVB*14]. However, the device is usable mostly for simple functions that have only few steps and are choice-oriented due to its small size [SAN01]. That is, with the prevalent interaction method being touch based, it is not easy to make fast and reliable input on small screen devices.
Various techniques have been proposed for facilitating simple text/command input (or icon selection) for small screened devices, using touch gestures, voice recognition, hand/finger written letter recognition, multi-layer keyboard, muti-page icon layout, and etc. [CCL15, KCC11, DSD*15, HHI*15, DKD14, FSH*14, OHO*13, BC09, AZ03]. In general, most of these extended methods require multi-step input (e.g. search and select) over several paged layouts, learning of particular touch gestures or modal input, and sacrificing interaction time over accuracy. This is a natural but almost unavoidable trade-off. In addition, many of these newly proposed techniques (focused on overcoming the small screen problem), have not been tested (or not many studies have looked into the usage) under the dynamic conditions for which smart watches was designed to be used effectively.