What are the #s & letters on the side for-W,6,5,4,3,2,N?

#s on the side of the greist buttonholer

My buttonholer has been making perfect buttonholes until yesterday and all my needles were broken.

I have an old treadle singer that has been converted to electric. I don’t know what the bar and letters and #s mean on the side of the buttonholer.

Maybe I have the wrong setting. I also put the plate on that has the hole for the needle to go through and I can see where the needles have hit and broken.

I have screwed the plate down securely but it is not helping. The needles are still breaking.

Also, someone said I need the tension set at 4. Is that the bobbin thread? I am only putting out suggestions. I am clueless but need to be making buttonholes soon.