When inserted into the socket-outlet at any possible angle (without applying undue force), the gauge shall cause lamp L2 to illuminate before lamps L1 and L3. When withdrawn, the gauge shall cause lamps L1 and L3 to extinguish before lamp L2.
The gauge shall be manufactured from hard, corrosion-resistant metal (e.g., stainless steel).
Standard:
IEC 60906-1 “IEC system of plugs and socket-outlets for household and similar purposes – Part 1: Plugs and socket-outlets 16 A 250 V a.c.” Figure 3

IEC 60906-1 Figure 3 Gauge for Outlets 16A 250V A.C.
Tags:GNGPL-90603