-8.0e-5 is temperature coefficient Zack calculated for the encoder arm.  This is seperate from the manget coefficient (-1e-3) which is taken out in the SXU EPICS software.    
Tried using this standrad -8.0e-5 factor and it didn't work, seems each SXU is different. The plots made using a standard Cell_GI.Calib_correction_factor_plus/minus = -8.0e-5 in Matlab program SXU_ISRDD_Cell_Summary are in this directory.  For more info see: LCLS-TN 20-1 "Temperature Dependance of LCLS-II Undulators and Phase Shifters"