private void threshold_parameter_set() {
        // choose different parameter setting
        // according to different bowlSize and number of players
        decreaseSpeed = decreaseSpeed;
        minimalShift = minimalShift;
        
        if(bowlSize < 20 ) {
            decreaseSpeed = 0.5;
            minimalShift = 0.00;
        }
        if(bowlSize >= 20 && bowlSize < 70) {
            decreaseSpeed = 7.5;
            minimalShift = 0.00;
        }
        if(bowlSize >= 70 && bowlSize < 300) {
            decreaseSpeed = 10.0;
            minimalShift = -0.02;
        }
        
        if(bowlSize >= 300) {
            decreaseSpeed = 10.0;
            minimalShift = -0.02;   
        }
        
    }