Instead of using a fishing line, I use a laser line. A vertical laser line.
The laser makes a vertical surface which can be used to change both camber and toe.
Just make sure the laser line is parallell to the car. I use two laser units and measure distance between the lines behind the car, and in front of the car on the wall.
To adjust the laser lines I now know that I have a difference in axel width of 10 mm on each side between front and rear axle. To measure this I use a steel scale and just count the millimeters from the center of the rim to the laser line.
Now it's time to start adjusting the car.
To check the toe-in you measure the rear of the rim to the laser line, and the front of the rim to the laser line.
And for the camber, you measure from the top of the rim to the laser line, and from the bottom of the rim to the laser line (sorry, I don't seem to have a picture of the scale at the bottom of the rim, but I think you get the picture)
Then I put in all the numbers in an excel sheeet to get total toe for front and rear axle, and camber in degrees (depending on rim size).
I'm sorry that the sheet is in swedish, but I hope you get the point here as well.