This article retraces the evolution of technologies for leucocyte differential, which is a key feature of hematology analyzers. It is emphasized here the way HORIBA Medical started using simple and robust technologies, based on CIS (Cell Impedance Signal) for 3 part DIFF, and then evolved toward more sophisticated bio-photonics designs including cut edge technologies, considered as pioneering works in the field of flow cytometry. This article was presented by myself at ISLH 2012, in Nice, France, at the luncheon session attended by about 200 worldwide customers.