Finger Correction D 

I was reading about it and it didn't make sense, so I figured either I don't understand what's written, or it's not very well explained. Thank you, this was very useful.

Amazing!

Thank you!

Here's a full lecture from this guy (Adrian Underhill) ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-1kAPHyHd7Lo.html

How could this work in a room with 35 students without exposing a student A LOT during the lesson?