... The HSL Algorithm for Reducing NICMOS Polarimetry Observations . ... The preflight Thermal Vacuum tests revealed that each polarizer has a unique polarizing efficiency, and that the position angle offsets differ from the nominal positions of 0, 120 & 240. ... I also present estimates of the NICMOS Instrumental Polarization, and discuss both the sensitivity of the Grisms to polarized light and the accuracy of NICMOS imaging polarimetry for faint and low polarization objects. ...