A way of denoting the emulsion position in 16mm film.
To identify a B-type on a winding bench the following formula is used:
Head to the right, perforations towards you and if the emulsion is upward then it is B-type.
Please note that this formula does not work for double perforation 16mm.
https://www.nfsa.gov.au/sites/default/files/uploads/2010/08/23/atype.jpg
References
© Kodak 1999