1 Use of digits and letters on telephone sets
2 Rotary dials
3 Push-buttons or keys
3.1 Ten push-buttons
3.1.1 Arrangement and numbering
3.1.2 Symbols
3.2 12 push-buttons
3.2.1 Arrangement
3.2.2 Symbols
3.3 Dual mode and engraving
3.4 Design of symbols
3.5 Position of figures, letters and symbols on push-button sets
3.6 Tactile identifier on the "5" button
4 Additional push-buttons for use on telephones
4.1 General
4.2 Specific recommendations
4.2.1 Register recall push-button