'Weight of touch' momentarily increases. The 'set off' process begins, moving the jack away from the roller in a grand piano, or from the notch in an upright piano. In both upright and grand pianos a spring is compressed or has its tension increased, and the top of the jack must overcome some friction in sliding out from under the roller or notch. In a worn or badly regulated action this can contribute an undesirable effect on the touch.