Instead of working with Hubble's constant, a common practice is to introduce the dimensionless Hubble constant, usually denoted by h and commonly referred to as "little h", then to write Hubble's constant H 0 as h × 100 km⋅ s ⋅ Mpc, all the relative uncertainty of the true value of H 0 being then relegated to h. The dimensionless Hubble constant is often used when giving distances that are calculated from redshift z using the formula d ≈ ⁠ c / H 0 ⁠ × z. Since H 0 is not precisely known, the distance is expressed as: