Precision in cosmological constant The observed cosmological constant, what is its precision? How precise do we know is it not a fluke or misinterpretation of cosmological data?
 A: The best values of the cosmological parameters available, are those published by Planck Collaboration 2018.
In it, the values of the Hubble constant and the dark energy density ratio are:
$$\displaystyle H_0 = 67.66 \pm 0.42 \, (km/s)/Mpc$$
$$\Omega_{\Lambda_0} = 0.6889 \pm 0.056$$ 
Remembering that:
$$\displaystyle \Lambda = \frac{3 H_0^2}{c^2} \, \Omega_{\Lambda_0}$$
We get for the Cosmological Constant the value:
$$\displaystyle \Lambda = 1.106 \times 10^{-52} \pm 0.021 \times 10^{-52} \, m^{-2}$$
The values of the cosmological parameters of Planck Collaboration 2018 are obtained from the CMB, that is to say, when the Universe was 380,000 years old and was composed exclusively of elementary particles without any star or galaxy yet.
Recently, The Dark Energy Survey (DES), studying galaxies in a sphere of 8,000 million years centered on us, (therefore objects of the universe at least 6,000 million years after the origin of the CMB), has obtained the same values, which makes these figures very robust.
More information at Dark Energy Survey reveals most accurate measurement of dark matter structure in the universe
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