Now you've got your reference points (in box form) set up around your car you can start to measure toe in / out on the wheels.
To measure the front wheel toe in / out the FSM states that you need to use a spreader bar to apply a force of 110 to 120N. I have actually seen other values of this force quoted such as 90 to 110N in the W126 FSM. Anyway I found this to be difficult to achieve without the special tool (000 589 18 31 00) – but I think I've come up with a pretty good compromise. Essentially if it were a vertical force the spreading force would feel like a 9 - 12kg weight. I have no way of measuring this but have a gut feeling that my DIY clamping device when turned into a spreader bar provides sufficient force for this job. This is a compromise and I can't be sure that it is good enough but it is the best I've got. I propped my spreader bar up on blocks of wood and used yet more wood to help reach the span between the front wheels.
Anyway to measure the toe in / out you need to measure from a fixed point on the furthest forward point on the rim to the string. Then measure from the furthest rearward point on the rim to the string. If these distances are the same then you have NO or ZERO toe in or toe out. If the furthest forward dimension is greater than the furthest rearward dimension then you have toe in. The opposite case is toe out.
To calculate the angle of toe in / out you need to remember the distance you had previously measured from the centre of the hub to the string (or measure it again). Then you need to measure the distance from the furthest forward point of measurement to the furthest rearward point of measurement on the wheel rim. This gives you the diameter – which divided by 2 gives you the radius – which can then be used with the wonders of trigonometry to get the angle. Use the formula sin ø = opp / hyp where opp is the difference between distance from rim to string and the distance from the centre of the wheel to the string, and hyp is the radius you've just calculated. If I were you I'd calculate both angles – the one that is forward facing and the one that is rearward facing – and compare them to make sure the angles are the same (you can also compare the calculated distances from the wheel centre measurement – if you see what I mean). They should be very close, otherwise check that your rim is true, or measure again.
WARNING:- If you move the axle stands that are holding the box of string around your car you are stuffed. You need to go back to step 6 above. The same is to be said if you move the car. In this thread whunter says you need to apply the brakes in order to obtain good consistent measurements:-
http://www.peachparts.com/shopforum/showthread.php?t=134630
I'm not sure of this (I think if you are careful it doesn't matter) but it would certainly help to hold the car in position – although using just 3 slip plates probably helps too. Perhaps the use of brakes needs to be discussed further?