Statoscope is a tool to plot graphs from data logged on a per-frame basis, and more generally, it's the system that produces and manages that data.
In essence, it provides a way of recording values (e.g. fps, number of drawcalls, etc.) from the CRYENGINE and showing how they change over the course of a play-through, and over several play-throughs.
Most of the tool functionality just controls presenting this data in useful ways, such as basic processing (averaging, local max), stats (min/max/average, buckets), comparison with other logs and in game screenshots and user markers for gameplay reference.
Currently there are three ways of displaying data:
User markers (vertical lines that show when infrequent actions occur, e.g. invalid file access, level load/unload).