I'm not sure why this doesn't exist, as this is the only app I've tested that doesn't allow you to create your own "metric" to track and graph (which is unfortunate, because this is one of my favorite apps that I've tested overall!) Most will allow you to create and name a metric and even allow you to customize the unit if it doesn't already exist. For example, you can currently track things like sleep, steps, etc. I'd also like to track daily overall stress levels, simply on a scale of 1-10, among other things.