Metal surface should be smooth and not be corroded by rust. Plating should not crease or peel off.

Plastic casing should not be uneven, crude or have any cracks or damage.

The insulation of different parts conducting electricity should bear the function of experiment voltage and there are no punctures on it.

90% of the surface will be covered by solder. Without deformation of base, can satisfy mechanical, electronic performance.

Action without blocking phenomenon, button allows the wear surface.