A typical industrial robot is built with fixed length segments that are connected either at joints whose angles can be controlled, or along linear slides whose length can be controlled. If each angle and slide distance is known, the position and orientation of the end of the robot arm relative to the base can be computed with simple trigonometry. Going the other way - calculating the angels and slides needed to achieve a desired position and orientation - is much harder. The mathematical procedure for doing this is called an arm solution. For some robot designs, such as the Stanford arm, SCARA robot or cartesian coordinate robots, this can be done in closed form. Other robot designs require an iterative solution.