The product is special auto transformer which is connected in different forms.Its output voltage can be regulated smoothly and continuously from zero to the maximum value.The provision of an indicating meter is made for the models TDGC 0.2,0.25,0.5/0.5(M).All the models find popular appliactions in industries,agriculture and scientific researches,and are particularly suited to serve as ancillary facilities for such equipment as various machine tools,transistor curve tracers,projecting TV sets,and analytical instruments in petroleum industry,etc.