Now repeat the process for Mirror #2 and mirror #3.
Apply a new piece of tape to mirror #3.
Use the UP AND DOWN arrows to move the gantry to the middle of the laser (from front to back), and use the LEFT arrow key to move the laser head all the way to the left side of the machine so the mirrors are closest together.
Press the PULSE button to get a scorch mark on the tape.
Use the RIGHT arrow key to move the laser head all the way to the right side of the machine and PULSE again.
Adjust mirror #2 until the scorch marks are in the same exact position on the left and right sides of the machine.
These two scorch marks should be in the same exact position. Being in the middle of the mirror opening is preferred but not necessary.
Next move the laser head with the ARROW keys to all four corners of the machine, pulsing in all four to ensure the scorch marks are in the same position on the tape.
If the scorch points all overlap each other, the mirrors are properly aligned, and you can move forward with the final step, the vertical alignment.