Viewing messages

I want an thing that will be useful for some people. Its the checkmark of messages. (Present on WhatsApp) Sometimes my friends just not see my message, and i want to know if they view my message. So, that will be useful to me and another people. The checkmark will be 3 balls, the onde ball is for sended, the second ball will be for sended, but not viewed, and the third is for viewed. Sorry for my bad english, but i think that its cool. Bye!