package brr

noticed is 0.1s, the time span after which the user will notice a delay and feel that the system is not reacting instantaneously.

interrupted is 1.s, the time span after which the user will feel interrupted and feedback from the system is needed.

left is 10.s, the time span after which the user will switch to another task and feedback indicating when the system expects to respond is needed.

feel () is a signal that varies according to user latency constants:

• [user_feel ()]_t = `Interacting if t < User.interrupted.
• [user_feel ()]_t = `Interrupted if t < User.left.
• [user_feel ()]_t = `Left if t >= User.left.

touch_target_size is 9.mm, the recommended touch target size in millimiters.

touch_size_min is 7.mm, the minimal touch target size in millimeters.

touch_target_pad is 2.mm, the minimum padding size in millimeters between two touch targets.

average_finger_width is 11.mm, the average adult finger width.