How your streak works
Your streak is the number of days in a row you have studied. Every day with a session, however short, counts and your streak grows.
Miss a day and your streak starts over at your next session. Your XP, level and statistics stay exactly where they were; only the streak itself resets. Cog looks sad for a moment, but gets over it quickly.
Tip: a short ten-minute session is enough to keep your streak alive on busy days.