Gorgeous, clean design, but then I’ve come to expect no less from you Paul. 
One suggestion for a feature- I actually discovered this myself just the other day. Basically, for that fullscreen graph view, it might be cool to mirror the functionality of the Stocks app graph view. If you’re in the Stocks app, you can turn your device into landscape and it will display a fullscreen graph (similar to yours). However, it has two cool features that might be neat to integrate into yours. 1, if you tap and drag in the chart, it will bring up a sort of scrubber that lets you view the exact value of that position of the chart (wherever your finger is). And 2, you can then tap with 2 fingers on the chart and it will display the profit or loss (along with percentage changes) for that region between your fingers.
It’s kind of hard to explain in writing, so just try it and you’ll see what I’m talking about. But anyway, I just thought that might be a cool feature to add, since it’s pretty relevant for an app like this.
But as always, keep up the great work!