1. Paul Cairns paul.cairns@york.ac.uk
ARMH: Fitts’ Law
Paul Cairns

2. A law?!?! One of the few in HCI Predictive Reliable
Valuable research tool!
ARMH: Fitts' Law

3. Today’s objectives Fitts’ Law Theoretical basis Adaptations for HCI
Implications for design
ARMH: Fitts' Law

4. Overview Model for prediction Time to point Difficulty of target
ARMH: Fitts' Law

5. A demo Interactive Fitts' Law talk Not quite accurate!
ARMH: Fitts' Law

6. Fitts’ Proposed Law D
1/W
a, b
Log?
ARMH: Fitts' Law

7. Theory (or Analogy?) Analogy with Shannon information
Meyer’s derivation
MacKenzie’s improvement
ARMH: Fitts' Law

8. Terms Index of difficulty Throughput, IP, 1/b bits bits per second
ARMH: Fitts' Law

9. Impact in HCI Reduce ID Compare IP Put things in edges and corners
Bigger icons, more space
Compare IP
“Capacity” of input devices
Put things in edges and corners
ARMH: Fitts' Law

10. Deconstructing Fitts Ecological validity Construct validity
ARMH: Fitts' Law

11. What Fitts did: W D
ARMH: Fitts' Law

12. Let’s have a go!
ARMH: Fitts' Law

13. What we apply it to:
ARMH: Fitts' Law

14. Dimensionality Fitts is 1d Does 2d matter?
not a lot!
Better models produce better fit
ARMH: Fitts' Law

15. Correcting for W W’ – actual cross-section Smaller of W and H
Area, W x H
Sum, W + H
Stick with W
Which is best?
ARMH: Fitts' Law

16. Implications debunked
Edges are better
Corners are best
Mice are non-linear anyway!
ARMH: Fitts' Law

17. Toolbars
This is annoying not useful
ARMH: Fitts' Law

18. What remains? D/“W” is key Non-linear (concave), monotonic
Target size (angle)
Stopping range (proportion)
Non-linear (concave), monotonic
Quite possibly log function
IP is meaningful
a is important
ARMH: Fitts' Law

19. Novel interactions Artificially increasing W Changing select
“Sticky” buttons
Bubbles
Changing select
Goal-crossing
ARMH: Fitts' Law

20. Novel devices Comparing throughput Fat finger problem! touchscreens
Wii
Kinect (in air pointing)
Eye Gaze
Fat finger problem!
ARMH: Fitts' Law

21. Thoughts on Modelling Is it a good model?
Yes, it fits the data
No, we don’t know why!
Could we produce a better one?
How?
ARMH: Fitts' Law

22. Advanced Fitts’ Law Fitts’ law as a model Steering law Games
Menu navigation
VE/VR?
ARMH: Fitts' Law

23. Reading for today
MacKenzie (1992) Fitts’ Law as a Research and Design Tool…, HCI (7),
MacKenzie & Buxton (1992) Extending Fitts’ Law to 2d tasks, CHI 1992,
Interaction Design, 2nd edn
Cockburn & Firth (2003) Improving the acquisition of small targets. BCS HCI 03,
Accot & Zhai (1997) Beyond Fitts’ Law… ACM CHI 97,
Bi et al (2013) FFitts Law.
ARMH: Fitts' Law