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The first electromagnetic Onuki-type undulator has been operating on the 800 MeV storage ring Super-ACO since spring of 1998. It consists of two crossed overlapped, 2.7 meter long, undulators able to produce any kind of polarized light in the VUV energy range with a switching rate of 1 Hz. The maximum magnetic field of 0.12 T is produced in both planes by the mean of bipolar /spl plusmn/210 A//spl plusmn/ 190 V and monopolar 210 A/135 V power supplies. The undulator producing vertical magnetic field can be shifted along longitudinal axis in order to change the phase of magnetic fields. Main design is summarized: mechanical structure, different sets of correcting coils, water cooling. Magnetic measurement results obtained by different methods are described, in particular, the timing of the beam transverse excursion according to the main current variations and the flux capture effect when the phase is changing. A good agreement was found between magnetic measurements, calculations and on-beam tests.