Continued photometric monitoring of the gravitational lens system 0957+561A , B in the g and r bands with the Apache Point Observatory ( APO ) 3.5 m telescope during 1996 shows a sharp g band event in the trailing ( B ) image light curve at the precise time predicted in an earlier paper .
The prediction was based on the observation of the event during 1995 in the leading ( A ) image and on a differential time delay of 415 days .
This success confirms the so called “ short delay ” , and the absence of any such feature at a delay near 540 days rejects the “ long delay ” for this system , thus resolving a long standing controversy .
A series of statistical analyses of our light curve data yield a best fit delay of 417 \pm 3 days ( 95 % confidence interval ) and demonstrate that this result is quite robust against variations in the analysis technique , data subsamples and assumed parametric relationship of the two light curves .

Recent improvements in the modeling of the lens system ( consisting of a galaxy plus a galaxy cluster ) allow us to derive a value of the global ( at z = 0.36 ) value of Hubble ’ s constant H _ { 0 } using Refsdal ’ s method , a simple and direct ( single step ) distance determination based on experimentally verified and securely understood physics and geometry .
The result is H _ { 0 } = 64 \pm 13 km/s/Mpc ( for \Omega = 1 ) where this 95 % confidence interval is dominantly due to remaining lens model uncertainties .
However , it is reassuring that available observations of the lensing mass distribution over constrain the model and thus provide an internal consistency check on its validity . We argue that this determination of the extragalactic distance scale ( 10 % accurate at 1 \sigma ) is now of comparable quality , in terms of both statistical and systematic uncertainties , to those based on more conventional techniques .

Finally , we briefly discuss the prospects for improved H _ { 0 } determinations using gravitational lenses and some other possible implications and uses of the 0957+561A , B light curves .