STL (settling time) is similar to follow through; however, its more sensitive and in my opinion a better indicator in tuning your machine. A perfect STL would be similar to a perfect follow through, which is 0% however, most machine won't hold 0% follow through constantly and this is normal. A machine running at 0% STL with an occasional 12-17% reading is fine. Since STL is more sensitive than follow through, this 12% reading may read as a 0% follow through any how. STL and follow through measure the contact action of your machine. In order to get a perfect 0% STL you need to eliminate any swiping action of the contact points. Generally, when adding speed or increasing tension to a machine will assist in achieving 0% STL. You can still get a machine to achieve 0% STL with a low speed and low rear tension, as long as you have a perfectly machined frame with and exact spring perch coil alignment and contact point hits flat on front spring. Check out my website for more info: www.SanMartinTattoo.com