Left Front
The left front caster block will have 7 marks across the top of it.  Each line is equivalent to two degrees of caster.  As you look down at the caster block, the line closest to the nose of the chassis is designated 12 degrees.  As you move towards the back of the chassis from there, each line decreases the caster by 2 degrees until you reach the final line, which is in fact 0.
 
The factor setting on dirt for our chassis is 8 degrees of caster on the LF.  One line "back" from center.
 
Right Front
The right front caster block is also designed with 7 marks etched in the top.  Again, these marks are equivalent to 2 degrees of caster per line.  For the right side, as you look down at the caster block, the line closest to the nose of the chassis is 14 degrees.  This is the maximum amount of caster available with the standard block.  Similar to the left front, as you move towards the rear of the chassis, the caster decreases by two degrees per line.  The line closest to the rear of the chassis is 2 degrees. 
 
The factory setting on dirt for our chassis is 12 degrees of caster on the RF.  Two lines "back" from center.
 
If you ever become confused and need an easy reference point to start from, stand both caster blocks up so that the line on the chassis is in line with the "middle" mark on the caster block.  This will be the 4th line (NOT DEGREE but ACTUAL LINE) on both the left and right side caster block.  When you place the caster blocks in this position, the caster will be 8 degrees on the RF and 6 degrees on the LF.  From here, you can adjust it accordingly.
 
Remember, the amount of caster you have in your chassis directly affects how much weight your chassis will transfer.  The larger the split, the less weight transfer you will have and the more your chassis will want to turn due to the difference of load on the RF compared to the LF.  On the other hand, the less split you have from RF to LF, the less the chassis will want to turn because the tires are more evenly loaded.
 
The amount of split that YOU need is going to vary on many factors.  99.9% of the time, we run between 3 and 5 degrees of caster split.  The best idea is to start at the recommended factory settings and once you have a solid baseline under the kart, fine tune with caster if you care to.