Firm foundation in the main hci principles, the book provides a working

Figure 4.20 A possible state-transition diagram for No Sheets.

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4.4.4 Interface Selection and Consolidation
We end this exercise by finalizing the choice of particular interfaces 
for the individual subtasks. Table 4.4 shows the final decision and jus-
tifications. It is very important that we try to adhere to the HCI prin-
ciples, guidelines, and theories to justify and prioritize our decision. 
Note that we have started with the requirement that the application is 
to be deployed on a smartphone (the interface platform). Again, our 
... want to show off my piano
skills ... but don’t have my
notes handy ...
oh yeah! my smartphone ...
Figure 4.21 Motivational context for No Sheets.
• Select song
• Select temp
• Play (Show chords)
• Show instruction
from a main menu/
screen touch
No Sheets
Select Song
Select Tempo
Play
Instruction
Figure 4.22 A typical usage scene 1: The top-level menu.

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initial choice will purposely not be well thought out, just to illustrate 
that a naïve and hurried choice would expose the application to be at 
high risk of eventually failing in terms of usability and user experi-
ence, even if it computationally satisfies the required functionalities. 
• Select song
• Select temp
• Play (Show chords)
• Show instruction
• Scroll and select by touch
• Finish by selection, OK, return button
from a main menu/
screen touch
Figure 4.23 A typical usage scene 2: Interface looks for three subtasks (e.g., song selection, 
tempo selection, and showing instruction).
Initial Play View
Hey Jude in C
C
- -
4
G
Information
view
Control
buttons
7
2
Don’t make
Hey Jude
–
Play
+
Play View (in paging)
(activated by pressing play button)
Fast forward during play
(activated by pressing + button)
Review during play
(activated by pressing - button)
Beep and vibration
at beats
Figure 4.24 A typical usage scene 3: Interface looks during “play” and the three concurrently 
activatable subtasks (play/pause, move forward, and move backward).

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Hey Jude in C
Select Song
Select Tempo
C
6
2
prelude
Play
–
FIN
Returning/Quitting
+
Instruction
No Sheets