BV9 septum coordinate system for G3 hall probe measurements. 

V notch exit pole:
 
x = 0 is the center of the width of the magnet
y = 0 is 30 mm down from magnet mid plane (or bottom of injected pole)
z = 0 is the edge of the pole extension.

Injection exit with mirror plate:

x = 0 is the center of the width of the magnet
y = 0 is 3 mm up from bottom of pole. 
z = 0 is the edge of the pole extension.

Injection exit without mirror plate along pole :

x = radius - sqrt(radius^2-z^2) + (-.0225 to +.0225 in steps of .0015), where radius = 7.8291 m
x is in the center of the width of the magnet at z =0.
x follows the formula x = radius - sqrt(radius^2-z^2) + (-.0225 to +.0225 in steps of .0015) 
to scan across the raised injection segment.  The data output looks like a scan 
from -.0225 to +.0225 in steps of .0015, but these x values have to be added to 
x = radius - sqrt(radius^2-z^2).  So at each z value 
x = radius - sqrt(radius^2-z^2) + (-.0225 to +.0225 in steps of .0015)
y = 0 is 3 mm up from bottom of pole. 
z = 0 is the edge of the pole extension.