I have been having lot of problems in get my program to work right due to matrix drift or errors. I,m using the PR_RotateEntity function and passing the rot_mat to the PR_Tranform which is used to transform the forward vector and the up vector for the camera. Here''s the problem chris, when I rotate the camera up and down several times and reposition the camera back to a 0 degree rotation for both x and y. I notice the test entity(earth object) is slightly tilted and offset from the screen. I have even checked the values of the entity rot_mat before rotating and after reseting back to 0 degrees for both x and y rotations, I notice a signicant error. This would account for the camera alignment error. Are you aware of this type of problem where the matrix has a tendency to drift. Is there a recomended way or technique for correcting for matrix drift. Thanks For Time Doug