The unit will recalculate your AVG and ES when you delete shots, but not the SD for some reason. If you send the session to the APP and delete the shots there, it will recalculate everything including SD. Odd little bug.
In fact, in the app you don’t even have to delete them. You can “ignore” the ones you don’t want in your calculations, and it will keep them logged but not use them in the calculations.