Hey, Jack.  You have the right idea, wait for the 3 green bars to settle.  When you first pick the string it can ring a little sharp.  So wait until after that initial onset.  Eventually you want to pick lightly enough to get it to ring without causing it to go sharp.  Here's a video on how to use it.

https://www.youtube.com/watch?v=Fg0ULlPvKJg

Hope that helps!