If in the measurement process of "follow the arrow, the deflection is large", if the deflection of the two measurement pointers before and after the inversion is too small to distinguish, it is necessary to "move the mouth". The specific method is: in the two measurements of "forward arrow, large deflection", pinch the junction of the two test pens and the pins with both hands, hold the base electrode b with your mouth (or press your tongue against it), and still The collector c and the emitter e can be distinguished by the judgment method of "forward arrow, large deflection". Among them, the human body plays the role of a DC bias resistor, and the purpose is to make the effect more obvious.