The control for the Position and Rotation Transformation Increments is on the Units tab of the Users Options.
These controls are used to adjust the relative position change applied when the up an down arrows are pressed in the Transform Objects control.
For example, in the image above, a position increment of 3 is set. Each time the up arrow in the X position is pressed and additional 3 units is applied to the current value. Conversely pressing the down arrow will adjust the position by a value of -3.
It can be helpful to change this increment value when trying to place an object based upon graphical display indicators. Using a value of 0.1" and 1deg would allow careful placement of an object using the arrow keys as an example.