When adjusting the dial with the mouse cursor it only moves in increments of 0.001. The feild actually acepts much finer adjustments - I can't remember exactly how fine off hand - but you have to type them into the feild by hand, double click on the value above the dial, then enter the desired value using the keyboard. A pose file can also be used to enter fine values, e.g:

{
actor leftEye
        {
        channels
                {
                translateZ ztran
                        {
                        keys
                                {
                                k  0  0.000255
                                }
                        }
                }
        }
}