The Redshift-Distance Equation.
We can readily observe Gravitational Redshift, for example light climbing out of the sun has all its wavelengths slightly shifted towards the lower energy ‘red’ end of the spectrum by the time it reaches us. For heavier stars, the effect becomes more pronounced. The gravity of the sun exists as a spacetime curvature which appears as an acceleration (a deceleration for anything trying to get away from it), this deceleration removes energy from light and causes a redshift.
Light traveling long distances across the universe becomes subject to its overall small positive spacetime curvature that also acts as a deceleration. This gives rise to a cosmological gravitational redshift in proportion to the distance travelled.
We calibrate redshift Z in terms of observed frequency over expected frequency and then subtracting one, so that the scale begins at zero rather than one.
Local galaxies have negligible cosmological redshifts. A redshift of Z = 1 corresponds to exactly half antipode distance. Light from near antipode distances has redshifts in excess of 10. Light from a luminous object at the antipode itself would have a redshift so high as to prevent its observation.