XQ - Perfect Lay Air Core Coil with varnish impregnation ERSE's perfect lay coils are the finest of it's kind. ERSE's perfect lay coils are wound with over 60 different precision orthocyclic tools on sophisticated computerized coil winders featuring hysteresis tension devices. What does this mean to you? Quite simply, the finest equally matched coil available today. This line of coils features 1% inductive tolerance. ERSE's perfect lay coils are excellent for those who do not want any saturation distortion, but still want a low D.C. resistance.