My understanding is that these cabinets were used for sewing and then a "writing desk" when closed. I have a 15-91 in that cabinet also but since I don't need a writing desk (actually have an old one) and don't use ink, I use that glass cup to hold straight pins. Love the machine and the cabinet. It was a gift to me from my husband after finding it in a local antique shop with a multitude of attachments in the drawers.