Illustration of integration orders in determining energy densities of cosmic components. The actual ICs are fixed by processes in the very early Universe, but we have only access to observables at specific later times (respective redshifts or scale factors). The values of the latter determine the value of H, and by extrapolation to the present the value of H₀. If H₀ determined by the CMB is used, it is this starting point (referred to as “CMB measurement”) which must be used in the integration of Eq. (3): values for the energy densities before this point in time have to be calculated using backward integration, while values for the energy densities after this point in time have to be calculated using forward integration. The green component has a time-dependent w, while the blue component has a constant w = −0.8.