Relation between the ﹩{\mathop{\sigma }\limits^{\unicode{x00304}}}_{{\rm{eq}}}﹩ and ∣v₀∣/Δv. ﹩{\mathop{\sigma }\limits^{\unicode{x00304}}}_{{\rm{eq}}}﹩ represents the enhancement of precision by mutual approximation; ∣v₀∣/Δv represents the ephemeris relative velocity at the central instant divided by the difference of two satellites’ apparent average orbital velocity. Values of ﹩{\mathop{\sigma }\limits^{\unicode{x00304}}}_{{\rm{eq}}}﹩ and ∣v₀∣/Δv are from Table 3.