Chain Break

Adjusting my chain today (first time). I used the hash marks on the swing arm. They were equal on both sides when I started so by moving them the same amount on both sides would keep my alignment. So, adjustment complete, hash line equal yet I now notice that the rear tire is very close to my chain guard. Less than 1/8" and closer to swing are on left side than the right. have no idea if it was that close before. Never checked. Is this normal? What is this plumb line method you guys speak of for alignment?

Found the plumb line method for wheel alignment.will give it a try in the morning. Would still like to know if it's normal for the left side of the tire to be so close to the chain guard. What is an reasonable distance to have there?

measure from center of the swingarm bolt to the center of the rear axle, both sides need to be the same