Inversely proportional to the cross-sectional area of the rod.
棒子的横截面积，成反比。
2
The relative reliable way is using fixed minor slope Angle of supporting rod or trestle and changing the height of camera to obtain different sample area.
认为比较可靠的方法是使用固定小倾斜角的支竿或支架，用改变高度调节取样面积。
3
The comparing result showed that the arc transition area between rod and head was easy to produce stress concentration which results in fatigue failure.