*3.1. Static Standing Trials*

The Pearson correlation between the forces index calculated from the force sensors during the static and dynamic trial (with different sensors combination) with the ink-type AI value is shown in Table 2. The highest correlation was found on the sensors at the medial arch position (sensor 5 + 4 + 3/2) with the Pearson correlation coefficient equal to 0.715. Meanwhile, the lowest correlation was found on Sensor 5 with r = 0.0707. The comparison between normal and flatfoot in the static trial is shown in Table 3. There is a significant difference between the normal and flatfoot force value in most of the sensor placement positions.


**Table 2.** Pearson correlation between the force sensor standing value and the ink-type AI value in the static test.

\*\* Correlation was significant at the 0.005 level (two-tailed).


**Table 3.** Comparison of normal and flatfoot pressure value in the static trials.

\* *p* < 0.05, significant difference, \*\* *p* < 0.005, significant difference.

## *3.2. Dynamic Trials*

The Pearson correlation between the maximum force index of the force sensor in the dynamic test and the ink-type AI value is shown in Table 4. The highest correlation in the dynamic trial was found on Sensor 5 with r = 0.801 while the less correlated sensor position in the dynamic trial was found in the Sensor 1 position with r = 0.063. The comparison of the normal and flatfoot pressure value and Mann–Whitney U test results in the dynamic trial is shown in Table 5. There was a significant difference between the normal and flatfoot pressure value in six of the sensor configurations: Sensor 3, Sensor 4, Sensor 5, 3 Sensor point (1, 3, 5), the medial arch sensor position, and the lateral arch sensor position.

The linear regression result from the AI vs. Sensor 5 placement in the dynamic trial is shown in Figure 8a. Those results had the highest correlation with r = 0.801 in the dynamic trial. Figure 8b also showed the worst correlation, which was obtained from the AI vs. Sensor 1 placement in the dynamic trial.

**Figure 8.** Arch index vs. sensor placement normalized force index in the dynamic trial. (**a**) The best correlation, which was obtained from the placement of Sensor 5; and (**b**) the worst correlation, which was obtained from the placement of Sensor 1.

Reliability analysis for the system measuring different trials on the same subject was done with an ICC two-way mixed model and Cronbach's alpha coefficient. The result showed that the proposed measurement system had high reliability for measuring different trials on the same subject with an ICC = 0.812 and Cronbach's alpha = 0.93.


**Table 4.** Pearson correlation between the force sensor standing value and the ink-type AI value in the dynamic test.

\*\* Correlation was significant at the 0.005 level (two-tailed).

**Table 5.** Comparison of the normal and flatfoot pressure value in the dynamic trials.


\* *p* < 0.05, significant difference; group effects were analyzed using the Mann–Whitney U test.
