Today, I do a formal pilot study to tune the parameter of the experiment, such as time arrangement, task difficulty and settings of the tablet.
First of all, I increased the task difficulty a bit, which I think could make the task harder to complete than before. Then, I also adjust some time arrangement, like resting time between two sections and between two figures as well. Finally, the angle of the tablet is tested by three separate pilot runs. Taking two factors into consideration -- the average pen pressure and the proportion of points which reached the pressure limit, I adjust the angle to be 30 degrees from the vertical plane.
Additionally, I also finish the consent form and the subjective ratings.