A plurality of direct memory access data transfers are accomplished to transfer data from a host to an adaptor. The device having a rod positioner for positioning the sucker rod and guiding a portion of the sucker rod into the sucker rod guide. A mount hole of rectangular cross section is formed at a specified distance in a specified direction from the nut. It makes it possible to increase the precision of the self-calibration with a smaller number of sensors than in the prior art.