Could someone kindly tell me why there are two thread guiding 'slots' on the top of the side plate of this machine? On nanjam's second photo, one on top left and one on top right, but as you sew at the machine, one in front and one in back. Thank you. I have been wondering this about my own 15 clone (avatar photo.) It is a simple stitch and as far as I know one-thread only, but I am missing something?