# Calculating J3 rotation relative to J2?

From any robot spec sheet:

I am assuming that the range of motion given for the J3 or 'U' axis is specified as a function of the position of the lower or J2 axis. Correct?

How do I find the absolute range of motion of J2 from the spec sheet? That is, what is the maximum positive and negative value that J3 can rotate? Because if I were to rotate using the range given for J2 then the arm would collide with the base.

I think from the spec sheet, it means that at some configurations, J3 could actually reach +255$^\circ$. For example, when J2 = -100$^\circ$, J3 may be able to reach that maximum of 255$^\circ$.

In other words, the range of J3, for example, depends on a specific value of J2. To find out the exact range of J3 given a specific value of J2, you may need a 3D model of the robot.