This application is designed to determine the amount of data being sent and received by the applications on your Android device in a controlled fashion.

Android exposes the Network Stats API which is only supported on Marshmallow and higher so as such this application requires a minimum API level of 23. Android also exposes a Traffic Stats API which works on pre-M devices but since that API aggregates all data per-app since boot it does not offer enough control for what this logging app is trying to do.

Aren't there thousands of these type of apps? There are many applications designed around checking you do not exceed your data allowance or checking data use in the last 7 or 30 days. There are far fewer apps out there which allow you to specify a specific time to start logging and then export those results for later analysis. Other apps will obsfucate how they tally up data usage, are difficult to verify and also group many applications into 'System' whereas I would like to have greater granularity than that.