Hi,

I am trying to use TRotation class member functions to rotate and transform one coordinate system into another. So I need my Z axis to be in parallel to the direction of gamma propagation and Y axis to be perpendicular to the ZX plane. I have initial gamma propagation and a cross product to find Y. I am trying the following,

```
TVector3 initial_gamma1_dir, intitial_gamma2_dir;
TRotation R1,R2;
initial_gamma1_dir.SetXYZ(0,0,50);
initial_gamma2_dir.SetXYZ(0,0,-50);
A_x_B = initial_gamma1_dir.Cross(initial_gamma2_dir);
R1.SetYAxis(A_x_B);
R1.SetZAxis(initial_gamma1_dir);
R2.SetYAxis(A_x_B);
R2.SetZAxis(initial_gamma2_dir);
```

… something like this.

Later I use R1 and R2 to transform the coordinate system.

My question is, does consecutive rotation using Set?Axis() overrides the previous one.

*ROOT Version:* 6.28/06

*Platform:* Ubuntu 22.04

*Compiler:* C++17