With a strut or contol arm suspension, the camber and caster are established by the location of the pivot points in 3D space. The steering axis allows only one degree of freedom and rotating the wheel from the straight ahead position will change the camber reading, but this is due to the effects of caster. Of course, when reading true camber the wheels should be pointed straight ahead. As the wheel is rotated about the steering axis, the camber reading will change. In fact, this is the way caster is determined!!!
I'm posting a copy of an e-mail reply (edited slightly for clarity) to another forum member who queried me this morning about how I align my cars.
BTW, I'm a retired automotive (GM) and aerospace engineer, and I've been road racing since the sixties (cut my teeth in a '63 Sting Ray) doing most of my own engine/chassis tuning/overhaul and modifications as required/allowed.
"You can use the inclinometer to measure camber directly by laying it against the tire or wheel flange. To measure
caster you take camber readings with the wheel at the left and right steering locks and the arithmetic difference is
the caster. Getting the sign correct can be tricky, especially on cars with near zero caster settings, but Mercedes
typically have high positive caster settings, so the number will always be positive. If you are patient you should be able
to read the inclinometer to less than 1/4 degree, but it can take repeated readings until you're consistent. As with
most things, competence comes with practice.
As an example, on the LH side, positive caster is indicated if the camber reading at full right lock is less than
the reading at full left lock, such as -3 and +7. The caster is 7 - (-3) = +10.
To set toe, mark the measurement point on both tires. Start with the marks at the rear and measure, then roll the car forward and measure with the marks toward the front. Align the marks as high as possible from the ground without the chassis interfering with the tape. Tires with straight circumferencial grooves are easiest to work with. With the
steering wheel straight sight down the tires to visually confirm that each has about equal toe in. Equal length tie
rods is also a reference check. I usually have to tweak one tie rod to get the steering wheel dead center when
traveling in a straight line after the initial test drive.
It's a somewhat lengthy and tedious process to do it this way, but I got tired of dealing with alignment shops that
wouldn't align the car to my specs and did not understand geometry, so I haven't seen an alignment shop for
about 20 years. I do experiment somewhat with different settings, but once I get alignment dialed in to what I feel
is optimum for handling, the settings hold indefinitely. As I said, on a W201 set the cam bolts on the lower
control arm for maximum negative camber and maximum positive caster. This will be achieved when the cam bolt
shanks are as far outboard as possible. Then take readings and equalize both sides. This will require you to set
the side with the greatest negative camber to equal the least and the greatest positive caster to equal the least by
rotating the bolts to move the shanks slightly inboard.
The front bolt controls camber and the rear controls caster, but there is some cross talk, so you have to do the
process iteratively. Shoot for camber of about -1 degree, if possible, and as much caster as you can get, which will
probably be in the range of 10-11 degrees.
The car must be on a level surface to do this, and most home garages suffice. You can use the camber gage to
check floor level. The control arm cam bolts should be tightened with the car at normal ride height so as not to
preload the bushings in torsion. It's tough to get a 150 lb-ft torque wrench under the car to tighten them with the
car on the ground, so I tighten them as much as possible with whatever wrench will fit, then put the car up on
jackstands to do the final torquing."
In a follow-up query I responded that you can buy a decent inclinometer from any good hardware or Home Depot type store for about $25 dollars.
P.S. The caster measurement is an approximation based on small angle geometric theory, however, the really important issue is to get as much positive caster as possible and have it equal on both sides. The more positive caster in the suspension the more "negative camber gain" you have on the outside front wheel in a turn. Negative camber gain helps offset body roll, which will keep the tire closer to vertical relative to the ground. This effect improves steering response and reduces understeer. More positive caster also tends to improve straight line tracking and on-center steering feel. Whether the true measurement is, for example, 10 or 10.5 degrees is not important - get as much as you can and equal on both side.