Among the things I routinely do wrong is thread my Singer treadle sewing machine. Threaded incorrectly, stitching produces a clotted mass of threads on the back.
My machine is a Singer model 66-1 with red-eye (also known as red-head) decals, produced some time after April 18, 1921.
![Singer 66-1 sewing machine](http://arts.piglet.org/wp-content/uploads/2017/11/8628DBD7-DEE8-4C46-AAEF-E6A64845D30B-300x225.jpeg)
I can tell the earliest possible date from the serial number, using ISMACS Singer serial number database.
![Serial # G 8719946](http://arts.piglet.org/wp-content/uploads/2017/11/CA1252E3-5EFD-4ADE-A0A4-554257EF2D27-300x225.jpeg)
Properly threaded, it runs like a dream. Do it wrong, however, and EEEEEEEEEEEE!!!
![Correct threading of Singer 66-1](http://arts.piglet.org/wp-content/uploads/2017/11/08B35663-EC2F-44B8-8F18-A82B2A694A4F-e1510514243212-225x300.jpeg)
I usually orient the bobbin correctly, but just in case I note here for future reference that the thread should exit the bobbin counter-clockwise when I drop it in, i.e., at the same angle as the slot in the bobbin case. Useful (and amusing) blog post about bobbin orientation may be found here.