When to call it a day

The other day after what was a very productive day of work for myself, as i passed my normal end of work day I began to ask myself when do i call it a day. I felt like I was getting so much done I was afraid to stop. When I took the time to think about it I realized this is not just a work questions but one that effects may aspects of life. I wanted to share a few of the tools that I use to know when to stop so that I can come back ready for tomorrow with the same enthusiasm.