We propose to improve the calibration of the Wind momentum - Luminosity Relationship of hot stars at solar metallicity by adding new objects with well determined distances, stellar parameters and wind momenta. We propose to acquire STIS low- resolution FUV spectra of O- and B-supergiants belonging to the same OB association to determine their terminal wind velocities. We selected stars in Cyg OB2, for which we alredy have optical observations and have performed analyses {or which are currently under way} with our model atmospheres codes to determine their stellar parameters and mass loss rates. A precise calibration of the WLR using objects of the solar neighbourhood is crucial for future applications of the method to determine extragalactic distances out the Virgo and Fornax clusters of galaxies.