Measures “distance” between the tool (instrument) and the object.
Spatial: How close the tool is to the object on screen.
Near → The tool is directly on the object (dragging it, grabbing a corner to resize).
Medium → The tool is near but separate (scrollbar next to document).
Far → The tool is somewhere else entirely (dialog box that changes the object).
Why it matters: Near tools feel more immediate and natural because you can see exactly what you’re affecting right where you’re working.
Temporal: How quickly you can start acting on the object.
Short → Immediate reaction (click and drag starts moving it right away).
Medium → You have to do a setup step first (select a tool in a toolbar, then act).
Long → Multiple steps before change happens (open a dialog, adjust settings, click OK).
Why it matters: Short delays feel more direct and responsive, long delays make interaction slower and more abstract.
Lower indirection = feels more immediate and direct.
Degree of Integration
Ratio = (DOF of instrument) ÷ (DOF of input device).
DOF stands for Degrees of Freedom — the number of independent parameters you can control or that can change at the same time.
Shows how well the input device matches the task’s requirements.
Ratio near 1 = good match; much lower means you can’t control everything at once.
Degree of Compatibility
How similar the physical action on the instrument is to the object’s response.
Higher compatibility feels more natural and intuitive (e.g., dragging an object moves it in the same direction your hand moves).
Low spatial offset + short temporal offset = you can manipulate the object directly, with no unnecessary steps or distance between your action and the visible change.