You can find the Application Performance Meter on the App page and in Analytics
Following a quick guide on how to interpret the Application Performance Meter:
The grade is like an energy rating grade (like electronic devices have in Europe) where A is the best (least consuming) while F is the most consuming.
The data for the Application Performance Meter is based on the life of the app
Legend: (only Analytics)
CPU=CPU-at-work-average data points / CPU-at-rest data points
RAM=RAM-average / RAM-max
Explanation based on the example above:
Data points occur every two minutes. So, out of 122 data points, meaning out of 244 minutes of working with this app, 116 (95% of the time) the CPU was high enough that we consider it to be doing something intensive ("at work"), while 6 of these 122 minutes (5%) were spent with the CPU being quite low, either because the person was typing some data or being a.f.k. or the app itself was waiting for something.
This is why the CPU-work bar occupies 95% of the circle, while CPU-rest occupies 5% of it.