How buttonhole sewing machines work - mandatory beginners

How buttonhole sewing machines work - beginners must know
Sometimes when we buy buttonhole sewing machines don't tell us how it works
This video I explained a little problem that is often experienced by novice operators who just bought a machine and confusion when the machine can not walk on the heavy pedal can not be completely stepped on
Also often after breaking the thread
Or after the thread doesn't turn the knife down
Please see this video
Hopefully this video is useful, at