One measure I use is what percentage of my time I'm actually working vs. doing other stuff (e.g. Twitter), another is how many distracting/annoying things I fin

One measure I use is what percentage of my time I'm actually working vs. doing other stuff (e.g. Twitter), another is how many distracting/annoying things I find myself thinking about (e.g. being hungry/thirsty, cold/hot, etc.).