There is a huge difference between evaluating a change in sound quality and knowing what you like to hear. We have a notoriously short audio memory and if we listen to a system that sounds "bad" long enough after a while it does not sound as bad. This is why you always trust your first impression. Fortunately distortion is easy to hear because it is so dissonant, sort of like looking for an elephant in a garage full of cars.
Rouliruegas, the best you can do is setting the bias with a test record. That is what I mean by correctly and yes it is not perfect. It can't be. there are too many changing variables you can not correct for. Viewing the cantilever angle just gets you in the ballpark and even that does not work well with very stiff cartridges like the Koetsu. Another neat trick to get you in the ball park is using a blank record. Cleopatra by the Lumineers is a three sided disk. The forth side is blank. You adjust the bias until the arm starts to drift backwards playing the blank side then fine tune with the test record.
Any arm without bias adjustment is trash unless you want to jury rig a bias mechanism for it. The primary problem is not sound quality or wear. It is tracking distortion. Any arm without bias is going to miss track the outside groove wall at lower velocities than a properly set up arm. Any good test record will demonstrate that. They are relatively cheap. Don't listen to me. Prove it to yourself. Oh, do not trust the gradations on the tonearms. They are good for reference. Cartridge jockeys can write down the settings so that when they change cartridges they can go back to the proper setting without having to go through the whole routine again.
Creed, I am an MD and can guarantee you I know a lot more about the brain than you do. You are not your brain. You as a psychological entity are a maze of bioelectrical reactions taking place in what is hopefully a brain. Soon it might be in a computer. I can damage your brain and disrupt those reactions and you won't be there any more but the brain still is. Alzheimers disease is a way of doing it slowly. Now, where you go afterwards is a matter of debate. Audio sales people are generally headed south.