from my alignment experiences , 11 years with chevrolet master technician
this is what i do on alignments
this is true in most cases
another way to somewhat think about it is a roof of a house is like a road ,
1 . think of it this way , as for caster if the vehicle has a perfect measurment on both sides left to right (wheel base wise) and you drive on a perfect flat road it will go straight , example a kids wagon
but that is not the case , the roads or hiways are designed not to hold water so there is a crown in the road ,so if you have a same measurment side to side it will pull to the right
now i know its hard to think about a f!@# , but when they were built back in the 20s and 30s , they were built with solid axles and NO adjustments , the way they solved the problem then was to , make the wheel base on the drivers side shorter than the passenger side , ex. pass side wheel base 110" and drivers side 109.5" , there fore the vehicle would tend to pull to the left all the time if in a perfect flat road ,so when on a road crown the vehicle would go straight , thus the reason for a positive caster on the drivers side
2 . camber , also goes with the road crown , if you put the camber at "plumb" or at zero , you will wear the drivers side tire out on the out side
due to the way the road is designed so the drivers side tire needs to be a little negetive , sounds crazy but i promise no tire wear , to much positive camber and the road crown the tires will wear out on the outside
3. toe , a way to look at it is this , look at your own feet if you face your feet together and walk for miles on end that way you will wear the outside of your shoes out , ex. / \ this is toe in . if the ouher way around it would wear the inside of the tire out ex. \ / this is toe out but if you were as straight as possible l l you would wear in a equal direction
a way i do it to rough it in when i do a frame off , until i can get it the the shop to align it is to set the toe with a tape measure , find o spot in the tread in front and measure and do the same in the rear till its within an 1/8 or 1/16 of an inch apart
hope this book helps