Here's a demo :
https://www.youtube.com/watch?v=wP-4EXZ-8Hw

The positive direction is defined by the vector starting at the first clicked point, and the mouse position in relation to it. From there, depending on these inputs, you might want to type +10 or -10 to move the object in the direction you want, away or closer to the other one.

In general MOI tends to behave as an hybrid of mouse-centric and key input-centric paradigms, requiring both at the same time when numerical precision is required (mouse for the direction, and kb for the input of values). Or, mouse-only for more improvised drafting. But AFAIK never keyboard-only.