Using pinion angle to measure castor

I need to check and probably adjust my castor and have found in the past that it is easiest to check the pinion and subtract the difference between the two to get the castor. Just to double check, is there a 9* difference between castor and the pinion angle or am I remembering incorrectly?

It depends on whether its a HP or LP.My notes show this:
HP>pinion angle+castor angle=9*
LP>pinion angle+castorangle=12*

It is high pinion so my memory isn't as bad as I thought! Thanks a million!

Dont forget that you will start with a negative number. So it not just adding 9 to -3 and getting 12. It is -3 plus 9 = 6 degrees of caster.
It is all on my site!