What are models good for?
good for mapping specific phenomena, with it being exactly as complex as needed
What is fitts’ law good for?
modelling pointing tasks; must be a single uninterrupted movement
what is goal-crossing?
Input model of drawing a line across a boundary, rather than pointing and clicking
pointing vs crossing
Pointing:
* control and correction at end of movement only
* Must stop within object
Crossing:
* control and correct all the way towards goal
* No need to stop within object boundary
advantages of cross-based selection
- easier to select objects that are thin
- multi-selection: move across multiple objects to select e.g. keys on keyboard
- good for input devices with no button to click e.g. head pointing
- good for when movement is jittery
Why are menu bars and key controls at the edges or corners of displays?
- Fastest to access from anywhere on screen
- Top of screen is an easy target
What is steering law?
The movement time to acquire a target through a tunnel e.g. multi-level drop-downs
steering law formula
MT = a + b * ID
What is the purpose of the Keystroke-level model?
Defines a set of basic input operators with time estimates for their execution
What are the 2 types of operators in the KLM?
Motor operators - moving hand from one object to another
Mental operator: mental preparation of a motor action
Advantages of KLM
- Easy to apply
- can be done from just sketches of an interface
- quite accurate
- useful for comparing alternatives
Limitations of KLM
- Assumes that the user is expert at task
- Assumes no errors
- not appropriate for tasks that require reasoning
