The left, right, top, and bottom insets are non-zero if there is any inset taking away screen space. For example, watches with a "chin" have a bottom inset that should be taken into account for properly center the drawing:
void setup() {
}
void draw() {
background(0);
translate(0, +wearInsets().bottom/2);
ellipse(width/2, height/2, 50, 50);
}