This machine is missing its safety ground. The strap should run straight back from the stud and under the metal board plane.
Here you can see how the missing ground strap should look. It runs from the ground stud to the back of the backbox, then up under the metal mounting plate.
A bigger view of ST:TNG. Upgraded speakers!
The CPU mounting screw is an OK place to put the ground strap if your machine does not have the safety ground properly installed, and you want to get up and running. But you should really add the ground strap!