The torque applied by the supply reel motor to keep the tape from freely spilling off the supply reel, and to maintain good tape-to-head contact.
"Just got my first order from you today. So far I have only heard it on a boombox but it sounds great. Since the records were in very good shape, it's hard to tell just what the sound restoration actually did, but it does sound very good. I expect to use your services again and will suggest you to my friends. Thanks very much."