Smartwatches and other wearables are characterized by small-scale touchscreens that complicate the interaction with content. In this paper, we present Force9, the first optimized miniature keyboard leveraging force-sensitive touchscreens on wrist-worn computers. Force9 enables character selection in an ambiguous layout by analyzing the trade-off between interaction space and the easiness of force-assisted interaction. We argue that dividing the screen’s pressure range into three contiguous force levels is sufficient to differentiate characters for fast and accurate text input. Our pilot study captures and calibrates the ability of users to perform force-assisted touches on miniature-sized keys on touchscreen devices. We then optimize the keyboard layout considering the goodness of character pairs (with regards to the selected English corpus) under the force-based configuration and the users? familiarity with the QWERTY layout. We finally evaluate the performance of the trimetric optimized Force9 layout, and achieve an average of 10.18 WPM by the end of the final session. Compared to the other state-of-the-art approaches, Force9 allows for single-gesture character selection without addendum sensors.

Lee Lik-Hang, Yeung Ngo-Yan, Braud Tristan, Li Tong, Su Xiang, Hui Pan

Publication type:
A4 Article in conference proceedings

Place of publication:
ICMI ’20: Proceedings of the 2020 International Conference on Multimodal Interaction, virtual event Netherlands, October 2020

force-assisted interaction, Optimization, smartwatches, Text entry

31 October 2020

Full citation:
Lik Hang Lee, Ngo Yan Yeung, Tristan Braud, Tong Li, Xiang Su, and Pan Hui. 2020. Force9: Force-assisted Miniature Keyboard on Smart Wearables. In Proceedings of the 2020 International Conference on Multimodal Interaction (ICMI ’20). Association for Computing Machinery, New York, NY, USA, 232–241. DOI:


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