1. Apparatus comprising: processor; computer readable storage medium accessible to the processor and bearing instructions which when executed by the processor cause the processor to undertake logic comprising: establishing an observation set of plural past ranges and respective past times between first and second objects to establish past range/time pairs; establishing a lookahead set of plural predicted future ranges and respective future times between the first and second objects; using a curve fitting routine, describing the past range/time pairs and future range/time pairs at least in part through coefficients or parameters of a mathematical model produced by the curve fitting routine; and outputting the coefficients or parameters to a third object to enable the third object to correct errors, common to both the second object and the third object, in range measurements.