Improvement of the calibration of the Cepheid period–luminosity relation (Leavitt's Law) is one of the main challenges to improve the accuracy of the Hubble constant, H0. Many parallax-of-pulsation methods are promising but have not yet delivered sufficiently accurate distances: observational biases, such as the projection factor, still dominate. We propose a global parallax-of-pulsation method, combining all observables (photometry, spectroscopy, and interferometry), to (i) reduce statistical errors, (ii) use the redundancy among observables to validate our approach, and (iii) achieve 2% accuracy for individual Cepheid distances.
