What is the correct angle for setting the tension.? There is not 1 correct answer to that. It depends on the quality and manufacturing of the scissor. In high quality scissors, the angle should be more open like in picture no 1 below. If the set (bow) and the rideline is made perfect, the 2 blades will perform perfect with each other. This is why the set of the scissor is one of the most important things to make correct on the scissor. Perfect set (Bow) and Rideline will allow the scissor to be set with a greater tension. (more tight like in pictutre no 1). This will not feel to hard for the hairdresser to cut with. On the other hand,- If the set (Bow) is made too big, poorly or wrong, the scissor can not be set with a greater tension. It will simply feel too hard for the hairdresser to cut with it. Then the tension must be set more like in picture No. 2.