Get yourself some 1/16" thick magnetic strips of sign material. Use two thicknesses for an upright and adjust the letoff so that when the hammer is held against the magnetic strip you push the backcheck forward until you can feel the just just brush the butt. You can taper this "feel" but I recommend you do not. Just adjust all the letoff to that specification. On grands you use 1/16" material and adjust the letoff with the hammer lifted against the magnetic material and adjust the treble so you can feel the jack rub the knuckle and taper this down into the bass so you can just know that the jack brushes the knuckle. This is very, very accurate and consistent. Exact specifications are not required, only exact consistency. All it takes is practice. Clear as coffee? Newton
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