  Polarization measures, on wide angular scales, together with anisotropy data,
can fix DE parameters. Here we discuss the sensitivity needed to provide
significant limits. Our analysis puts in evidence that a class of models
predicts low correlation or anticorrelation between polarization and anisotropy
at low l. This class includes open models and models with DE due to a
Ratra--Peebles (RP) potential. Results on this point, given in a previous paper
of ours, are updated and partially corrected. We outline that, with the
sensitivity of experiments like SPOrt or WMAP, high values of Lambda (energy
scale in the RP potential) can be excluded. With the sensitivity expected for
PLANCK, the selection will extend to much lower Lambda's.
