The traceability of direct current ratio based on the principle of difference measurement is usually an effective way to meet the requirement of measurement uncertainty. However, the shortboard with the ratio adjustable resolution limits the application range of practical traceability. In this article, we propose the concept of equivalent fractional turns, establish the mathematical model of deep adjustment, break through the bondage of the ratio minimum step value under the existing theory, and realize the direct current ratio conversion device with the characteristics of multi-disk linkage with the resolution 1 × 10 -9 and the error superior to ± 2 × 10 -7 . The nominal ratio value of two standard devices is adjusted after linkage to be consistent with the calibrated one and solve the problem of full step value traceability within the range. A self-calibration method based on the reference winding is proposed for this conversion device. The difference value among the primary winding, reference winding, and secondary winding is measured in proper order. We correlate the error between the disks and obtain the actual ratio value of any disk at any position, which is characterized by real-time reproduction without relying on the upper standard device.