Coordinate System:

Z = 0 is the longitudinal center of the solenoid
-Z is toward the + terminal
+Z is toward the - terminal

X = 0 is defined by the center of the bore
+X is toward the + terminal

Y = 0 is defined by the center of the bore
+Y is toward the - terminal


The Hall probe measures the field in the -Z direction.
With current flowing from the + terminal to the
- terminal, the field is in the +Z direction, giving
negative Hall probe readings.