# Haptic Soft-Keyboard for Tablet-Sized Touchscreens
## 4 Results
Well-known metrics, key strokes per character (KSPC), words per minute (WPM), and uncorrected error rate (UER) [1; 17; 22], were used for quantitatively measuring typing performance  
Figure 8: Acceleration values (left) measured on a 10.1 inch touchscreen with a three-layer piezoelectric actuator as a function of input voltage (Vpp) for two conditions, free stroke on a detached touchscreen (right) and after embedding the actuators in a tablet. across two conditions, visual (V) only and visual and haptic (VH), to see the effectiveness of tactile feedback when adding to an existing soft keyboard. The two conditions were counterbalanced and randomized. For the V condition, the pressed key was highlighted in white, while tactile feedback was additionally provided for the VH condition. The experiment consisted of ten blocks per condition, and each block had fifteen sentences that were randomly selected from a phrase dataset created by [23]. Each sentence was displayed in red at the top of the touchscreen, as seen in Figure 9, until the user finished transcribing the displayed sentence. The white text box showed what the user typed in real time. Ten participants (six males and four females, average 24.2 years old) took part in the experiment. All participants were skilled typists and had at least two years of experiences using the soft keyboard of a 10.1 inch tablet device. Before starting the experiment, a training session (about 5-10 min) was provided to participants to get familiar with the tactile soft keyboard. Each participant was then instructed to transcribe displayed sentences as quickly and accurately as possible. The participants wore earplugs to block noise during the experiment. It took about fifty minutes for each participant to complete the experiment. Figure 10 shows the results of typing performance (KSPC, WPM, UER) tested with the haptic soft keyboard. The bars represent the average values of each metric obtained from the experiment, and the error bars show the standard deviations. Note that a lower value meant better performance, except with WPM, which was interpreted as typing speed. As an efficiency index, KSPC ranged from 1.17 to 1.38, with VH appearing to be more efficient, which showed better productivity when tactile feedback was added. The average UERs, typing errors, were 0.54 and 0.8 for VH and V, respectively, which demonstrated improved accuracy with tactile feedback. In contrast, there was no difference in typing speed observed from the average WPM values from 28.4 and 28.9 for V and VH, respectively. A one-way ANOVA showed that there was no significant difference (\(p>>0.05\)) across conditions for the three metrics. Figure 9: Soft keyboard design and a user interface implemented on the Android platform with a 10.1 inch commercial touchscreen (uPad) for a user study. The white text field was an area for a user to transcribe a red sentence randomly selected from a test set of sentences created by [23]. For the visual (V) condition, the pressed key was highlighted in white, while tactile key click feedback was additionally provided for the visual and haptic (VH) condition.