With a little more digging on this I think the issue is down to the
default calibration values.

I have further confirmation that this is due to the calibration used when
the dial is presented via the joystick interface. The values in the event
interface are correct.

See 'joydev_correct()' from 'driver/input/joydev.c'

The problem is that the 'broken line' calibration can not properly
represent/process a value with a small range - I guess this does not
matter when there is a large input range.

In my system I have a dial (RZ) with 4 positions (0..3):
      expect to see -32768, -10922, +10922, +32768
      actually see -32768, 0, 32768, 65536 (limited to 32768)

Anyone got suggestions?
Simon

--
More info:

jscal -s 8,
        1,0, 0,0,298261,298261,                 // Wheel = -1800..1800
        1,0, 511,511,1050628,1050628,           // Throttle = 0..1023
        1,0, 511,511,1050628,1050628,           // Brake = 0..1023
        1,0, 5,5,107374182,107374182,           // RX = 0..12
        1,0, 5,5,107374182,107374182,           // RY = 0..12
        1,0, 1,1,536870912,536870912,           // RZ = 0..3
        1,0, 0,0,536870912,536870912,           // Hat = -1..1
        1,0, 0,0,536870912,536870912            // Hat = -1..1
                /dev/input/js0


from driver/input/joydev.c
--
        case JS_CORR_BROKEN:
                value = value > corr->coef[0] ? (value < corr->coef[1] ? 0 :
                        ((corr->coef[3] * (value - corr->coef[1])) >> 14)) :
                        ((corr->coef[2] * (value - corr->coef[0])) >> 14);
                break;
--
        case JS_CORR_BROKEN:
                if (value > corr->coef[0]) {
                        if (value < corr->coef[1]) {
                                value = 0
                        } else {
                                value = ((corr->coef[3] * (value -
corr->coef[1])) >> 14)
                        }
                } else {
                        value = ((corr->coef[2] * (value - corr->coef[0]))

quoted

14)

                }
                break;
--

        RZ = 0,1,2,3 :
                expect to see -32768, -10922, +10922, +32768
                actually see -32768, 0, 32768, 65536 (limited to 32768)