The uncertainty values used within the HIPS Vessel File need to be entered as 1-sigma. This being the uncertainty of a sensor.
Throughout the TPU Resource page there is reference made of uncertainty in several different forms such as 95%, CEP, RMS, etc. It must be remebered that HIPS and SIPS requires the 1-sigma value to be entered in the Vessel File for a more rigorous computation of the TPU. Below are some of the relationships between the 1-sigma value and some of the common values found in manufaturer's specifications.