A rate locked loop (RLL) regulates phase slip between two clock signals to provide precision timing for radar, TDR and laser ranging systems. Two clocks having a small mutual frequency offset exhibit a slowing changing relative phase, or phase slip, that produces a stroboscopic time expansion effect in a ranging system. A phase detector converts clock phase to voltage and the voltage is differentiated to provide a rate-of-change signal to a loop controller that precisely regulates the rate-of-phase change. The RLL controls a VCO to produce a constant, linear phase slip having phase errors below the time equivalent of 1-picosecond.