This book is dedicated to descript the Complex Numbers Square-Rooting Unit. In this book a little-known theory of complex number coding is being used. Included is a brief outline of theory of coding and calculation method which is a generalization of the "digit-by-digit" method for complex numbers codes. The algorithm of square root extraction from complex number is detailed, as well as its hardware implementation and simulation in the MATLAB system. The simulation in the MATLAB system of several known algorithms of the "digit-by-digit" method is also described. The open codes of all the said algorithms are enclosed.