The FemtoStepper™ is a high-performance, high-resolution phase & frequency synthesizer. It features an advanced <100 fs resolution step to control and adjust the output drift of a master clock without changing its behavior. It is designed for clock ensembling modeling and physical time & frequency generation from a clock ensembling system. Applications include the generation of time system in metrology labs, satellite navigation system, and time generation like Galileo's primary time facility or Doppler shift compensation to name a few.