Switch to the 10X objective into the optical path. Without using the coarse and fine focus knobs, adjust the focus on your dominant eye using the diopter rings.
Next, turn the diopter correction ring with the eye opposite to the reference eye to focus.
When focusing the 10X objective lens, slowly rotate the diopter correction ring on the left and right eyepieces, and adjust to the optimal position so that there is no diopter difference between the left and right eyes even when switching from the objective lens 10X to 40X.
Completing the diopter adjustments
Your adjustment is complete if you do not feel any differences between your left and right eyes when you look into the eyepieces using the 10X and 40X objectives.