The gauge when inserted into the socket-outlet, without undue force but at any possible angle, shall cause lamp L2 to light up before lamps L1 and L3.
The gauge, when withdrawn, shall cause the lamp L1 and L3 to extinguish before lamp L2.
The gauge shall be made of hard corrosion-resistant metal (e.g. stainless steel).
IEC 60906-1 Figure 3
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