Actually there are formulas for figuring this. Last I checked a Vector3 in Unreal is simply an x,y,z value group. It treats all vectors as having an origin at the center of 3-space and then a displacement is added as needed. All you need to do is treat just one of the vectors above as coming from that origin of (0,0,0) - probably A. I’d treat B as having an origin being displaced to A’s terminus and C’s origin being displaced in the same manner relative to B. That will make the line BC a reference line for determining an angle. Just connect a line from A to BC where angle ABC is 90 degrees. Call this point of intersection P. Then you have to make a decision about which angle you want to consider as the basis of your rotation. PAB or PAC. A is the origin of a sphere where BC is a tangent to that sphere intersecting with the surface at point P. Not having a use case I can’t go any deeper.