A Unique Measurement of the Top Quark Mass using the Decay Length 
of the b-quark in $t \rightarrow Wb$ Decays

We have developed a novel method to measure the mass of the top
quark using the transverse decay length of b-hadrons from top
decays. This technique relies solely on tracking and thus avoids
the jet energy scale uncertainty that is common to all other
methods. We have applied this new method to a lepton+jets top sample
corresponding to 1 fb$^{-1}$ CDF data and have measured a top quark 
 mass of $183.9 +15.7- 13.9 (stat.) \pm  5.6 (syst.)$ GeV/$c^2$. 
While this result is not a competitive measurement by itself,
since the decay length technique is highly uncorrelated with other
methods, it already plays a significant role in reducing the overall
uncertainty on the top's mass in combination with other CDF measurements.
The method, the results, and the current and long term impact on top mass
measurements, at the Tevatron and beyond (LHC), will be discussed.