Life Line Number representation

Hello, what is the difference between lifeline representation between 1 and 1.1 with 1 and 2 ?

House System.png

Dear Peter,

Thank you for your message. The message 1.1 appear is because the incoming and out going message of Personal Planner Profile lifeline are under the same activation. We consider this is a nested call therefore showing with sub-message number 1.1. For message 2, since the it is out going from another activation, therefore it is start with a new number instead of a sub-number. Details sample about numbering can be found in the attached image. Feel free to contact me if you require any further information.

Best regards,