Measure the Hubble Constant (aka Freedman et al. (2000)).
From the Introduction (section 1):
Quote:
The previous 29 papers in this series have provided the distances to individual galaxies based on the discovery and measurement of Cepheids, discussed the calibration of the data, presented interim results on the Hubble constant, and provided the calibration of secondary methods, and their individual determinations of the Hubble constant. A recent paper by Mould et al. (2000a) combines the results for secondary methods (Gibson et al. 2000; Ferrarese et al. 2000a; Kelson et al. 2000; Sakai et al. 2000) with a weighting scheme based on numerical simulations of the uncertainties. In this paper, we present the final, combined results of the Key Project.
[...]
Establishing plausible limits for the Hubble constant requires a careful investigation of systematic errors. We explicitly note where current limits in accuracy have been reached. We intend this paper to provide an assessment of the status of the global value of H0.
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For our purposes, the Mould et al. (2000a) paper is (very likely) worth reading; but let's start with §2 and §3, a summary of the method and determination of Cepheid distances. After that, we could consider the van Leeuwen et al (2007) paper as it relates to Cepheid distances, before moving on to §4 and §5 (where Freedman et al. apply a nearby flow field correction and "
compare the value of H0 obtained locally with that determined at greater distances").
Then we could take a look at the secondary methods (§6 and §7, plus Mould et al. (2000a), van Leeuwen et al (2007) again, and some of the other papers mentioned in the OP). If we're still on track after that, or perhaps in conjunction, §8 should become highly pertinent ("
The remaining sources of uncertainty in the extragalactic distance scale and determination of H0").
OK?