In order to get calibration parameters use unit/get_accelerometers_calibration:

svc=unit/get_accelerometers_calibration&params={"itemId":<long>}

{
     "acceleration":           /* acceleration calibration coefficients */
         {
           "coef_x":<double>,    /* coefficient by x-axis */
           "coef_y":<double>,    /* coefficient by y-axis */
           "coef_z":<double>,    /* coefficient by z-axis */
           "cos":<double>,       /* cosine of angle between theoretical and extimated axis */
           "sin":<double>        /* sine of angle between theoretical and extimated axis */
         },
     "brake":{ ... },         /* brake calibration coefficients */
     "turn":{ ... },          /* turn calibration coefficients */
     "vertical":{ ... },      /* vertical axis calibration coefficients */
     "crc":<uint>,            /* accelerometer sensors check sum */
     "dateinput":<uint>       /* calibration date */
  }

If accelerometer is not calibrated then {error:0} returned.