Usability Analysis

1. Task: Find contact Lynda in cell phone contacts book

2. Buttons: (▼), (2ABC), (3DEF), (4GHI), (5JKL), (6MNO), (7PQRS), (8TUV), (9WXYZ), (0)

3. Notation: ↓ -press ↑ -release * -repeat task s -seconds to complete

CASE #1 - Motorola RAZR V3

[(5JKL)↓↑ *3]3s [(▼)↓↑ *12]8s = 15 operations over 11 seconds

CASE #2 - Nokia N80

[(5JKL)↓↑ *3]3s [(9WXYZ)↓↑ *3]3s [(6MNO)↓↑ *2]1s = 8 operations over 7 seconds

4. Analysis:

In case #1, people use name initial to find the the first contact with the same name initial as the one looking for, and then press down key to find the right one. The number and time of operations depends on the length of contacts list. If a contact is at the end of a long sub-list, it will take many repetitive press operation and consequently long time. And it's very annoying that one have to go through many unwanted contacts to find the wanted one.

In Case #2, people filter the contacts by spelling out the name, which is a very natural and direct way. Also, numbers and time of operations are independent with the length of contacts list.

5. Suggested Improvement

With the above comparison, the way of Case #2 is superior. Further, the longer the contacts list is, the more obvious that Case #2 outperforms Case #1. But still there is improvement space.

In Case #2, say one wants to find the contac "Lynda", he will press "2JKL" button 3 times to get letter "L", and "9WXYZ" button 3 times to get letter "Y", and "6MNO" 2 times to get letter "n", and so on. The numbers of operations can be reduced a lot by bringing in auto-match feature. For example, if on my cell phone, I only need to press "2JKL" button once and "9WXYZ" once and will get "Lynda" and "Kydi", which are two possible matches of these two buttons.