Measuring X & Z coxa offsets for phoenix IK

  I need to enter some IK measurements into the arduino code for using the phoenix system with my hexapod. Ive measured the coxa length, femur length and tibia length but im a lil confused about measuring the coxa offsets. Especially since some are in the negative on the config.h file found here................<p>

https://github.com/KurtE/Arduino_Phoenix_Parts/blob/master/Phoenix/Chr3_Commander_SSC32/Hex_Cfg.h

I think X is always from the center line to the coxa but how do get Z coxa offset and why are some in the negative? Like the first measurement Right front coxa servo X.