Not as tough as I thought it would be.
Using a Sears Craftsman level/laser measuring tool or any laser level.
A small cardboard box.
You need a bike centerline reference.
I used the front wheel, so the front end has to be STRAIGHT!
This was the most time consuming part.
I marked a horizontal line across the box and a vertical centerline. Then made vertical lines 2 inches each way from center (dammit not micro 0.0009 perfect, just make the lines about every 2 inches!).
I put a 2 inch block under the kickstand to get the bike closer to vertical, but straight up is not a requirement. AND HEY, IF YOU DO THIS DON'T DROP THE BIKE!
Straighten the front end:
Measured from the handlebar hex bolts in the grip endcaps to the pax peg mount upper retention bolt. I use these since they are in the same place on both sides of the bike. I don’t know if they are accurately machined to be the same place on both sides, but I used them anyway.
Getting both handlebar ends the same distance took more time than I thought. Not hard, just a little tedious.
Then I used the level to sort of shim up one side of the box with just about anything (I used the laser level pouch) to match the angle the bike was leaning on the kickstand. Doing this is why the bike doesn't have to be exactly vertical.
Once you have the bars set, you can shoot the box from both sides of the FRONT tire, divide the distance, and match up the box centerline with the centerline of the front tire/bike.
So now I had a target in front of the bike and could shoot a relatively straight, measured line.
I just slapped the level on one side of the back tire and shot a line to the box. Noted where along the measured line the shot fell, and then put the level on the other side of the tire and shot that side.
The shots were off less than half inch from each other with the box at 4 feet in front of the bike. Close enough for me. I was surprised it was that close and did not make any adjustments. I suspect that if you do need to adjust the rear axle, it would take a bit to go back and forth to check it with the lazer. Rather than that, I recommend doing this or some other semi-reliable method once to calibrate the swingarm marks and go from there.
This took about three times as long to type as it actually took to check the tire.
The rear axle adjuster marks and swingarm dots are more accurate than I expected. Maybe not perfect, but certainly close enough not to wear things faster than needed.
I went though all this because I’m leaving on a 3500 mile trip next week, the bike has 25k miles on it, and so do the chain and sprockets. They still look good, but I have a new set in the box ready to install, I didn’t want to replace them just for grins. I did want to assure myself the chain is as straight as I can get it in the garage.
The
Craftsman Lasertrack I used.
An
El-Cheepo (that's a Mexican brand name, El-Cheepo... never mind

) level that I have one of that would probably work better. Any laser with a measured level side will work.
If someone else posted this already, sorry for taking up so much space. The tires are too different in size for me to get the string thing to work.