There are a few ways of doing wheel alignment, from complicated method with simple tools, to simple method with complicated tools. Its up to a workshop's decision on what tool to use for doing wheel alignment, they cost different in money, and different in time, energy and quality. depends on which part you value more.
Tradition method
Wheel alignment history could be as long as human civilizationm when Chariot firstly recorded in history book about ancient Rome.
Charoit is the origin of modern transportation, the track size and the direction function of front wheels, affect the design of modern transportation method. like railway system, vehicle system etc. There shall be wheel alignment specification for each charoit too, base on the design. It was possible that they use tape meter to do wheel alignment. and this method is still applicable for doing wheel alignment for modern cars, search youtube and you will find some video about this method. but frankly speaking, this way is pretty difficult for the car you drive, and it require your deep knowledge of wheel alignment, because the structure of suspension of vehicle is too much more complicated than it used to be. To realize wheel alignment with tape meter, cost you no money, but will cost you a lot of time, and accuracy is not assured.
Laser Wheel alignment
Then, there is laser wheel aligner, for determine the angle(or in MM). from one wheel position to another. can do the adjustment with reference to a special databook.
the result done by this way, is very nice, except that it can not do wheel compensation, to elimate the errors.
CMOS/CCD wheel aligner
CMOS camera was widely used in 1990s, on wheel alignment system as well, then we have CCD wheel aligner, in that CCD is more accurate and less affect by the sunlight.
CMOS and CCD wheel aligner carry the same methemetical model:
By equipped with vertical tilting sensor, the camber of each wheel could be detected. and by wheel compensation, the errors could be eliminated. and the clamps are important to assure the accuracy.
8 toe 4 wheel wheel alignment is the most complete measurement by checking the status of each wheel with reference to other wheels. while 2 toe 2 wheel alignment is not accurate, because it neglated the thrust angle.
3D wheel aligner
Now 3D wheel aligner attract more and more attention, in that it offer more durability and stability for the wheel aligner itself. and reduce the spread cost of wheel alignment in the long run. another good news is, 3D wheel aligner doesn't require a set of good clamp.
3D wheel aligner adapt 3D dimension methemetical model to calculated on the B/W target picture captured by the cameras at more than 20 FPS. and get all the parameters by calculation.
The biggest difference between 3D and CCD is, 3D adapt 3 dimension( axis x, y, and z).
The vehicle shall have same data inside the camera range. but most 3D wheel aligner manufacturer havn't solve this yet. instead, they fix one or few height point. when they ask you to calibrate the wheel aligner at a fixed height, or ask you to calibrate it at more than 1 height level. they just not solve this yet.
Contactless wheel aligner
Contactless wheel aligner is the future of wheel alignment system, but apprently, it will take many years to realized and be available for a regular workshop.
Appendix
Compensation
Wheel compensation is used in CCD and 3D wheel alignment system, to eliminate the error caused by the flat level of the wheel surface. there are two kinds of compensation method used, to realized the same function:
Push compensation
The compensation of wheel was done by push the car backward and forward. mostly apply to 3D wheel alignment.
Turn wheel (run-out) compensation
The compensation of wheel was done by turn each wheel 90 or 180 degree. mostly apply to CMOS/CCD wheel alignment. In that, push a car with sensors on, increase possibility of damage the sensors.
Leslie