Table 2: Form classification and feature coding.

ClassForm features

A {A1. linear, A2. convex arc, A3. concave arc, A4. prominence waist}
B {B1. 1 : 1~1.5, B2.1 : 1.5~2, B3. 1 : 2~2.5}
C {C1. thinner, C2. thin, C3. thick, C4. thicker}
D {D1. independent to function keys, D2. combination with function key, D3. partly overlap with function keys}
E {E1. small R angle arc, E2. arcs, E3. arc-shaped}
F {F1. straight, F2. Small arc, F3. big arc}
G {G1. 1 : 1, G2. 1 : 1~2, G3. 1 : 2~3, G4. other (large screen)}
H{H1. rectangular, H2. oval shaped, H3. round, H4. other geometric shape, H5. divided by the surface shape}