We report on an observing campaign in March 2001 to monitor the brightness of the later arriving Q0957+561 B image in order to compare with the previously published brightness observations of the ( first arriving ) A image .
The 12 participating observatories provided 3543 image frames which we have analyzed for brightness fluctuations .
From our classical methods for time delay determination , we find a 417.09 \pm 0.07 day time delay which should be free of effects due to incomplete sampling .
During the campaign period , the quasar brightness was relatively constant and only small fluctuations were found ; we compare the structure function for the new data with structure function estimates for the 1995–6 epoch , and show that the structure function is statistically non-stationary .
We also examine the data for any evidence of correlated fluctuations at zero lag .
We discuss the limits to our ability to measure the cosmological time delay if the quasar ’ s emitting surface is time resolved , as seems likely .