The multiple reflection within the circular disc provides a design feature to reduce the influence of non-total internal reflection and significantly improves the measurement linearity.
光线在圆盘内的多次反射显着地消除了非全内反射的影响,有效地改善了测量线性度。
In this paper, we point out that there exists a logic problem to calculate the area of circular disc in many textbooks of calculus.