The jet energy resolution comes from many sources, which can be
grouped into two categories, detector and physics effects.  We studied the
physics uncertainties using simulated W --> jj events in order to improve the
low-mass tail in the di-jet mass distribution.  For the detector resolution
we used both CDF detector simulation and data.  For the first time the full
granularity of the CDF detector is used to perform corrections at "tower
level" rather than at "jet level."  The track momenta measured by the
Central Tracking Chamber (CTC) and the neutral cluster energies measured by
the Central Shower Max (CES) are used to correct the calorimeter tower
energies.  When tested on gamma + jet data, our new algorithm has shown an
improvement on the jet energy resolution better than 20% compared to the
standard CDF jet corrections.