Relative deviation of view factor F₂₁ with respect to M₄ for two facets sharing an edge with a 60° opening angle between them, shown as a function of subdivisions of the two triangles. Only the two M₃ methods are dependent on the number of subdivision. Both M₃-Linear and M₃-R2 become more accurate with larger number of subdivisions. We find that around 100 subdivisions the deviation from the reference is about 10% for M₃-Linear and about 5% for the M₃-R2. However, the M₃-R2 is unpredictable for very small number of subdivisions (see text for details).