↩ 🔵 🔵 🔵 ❪✺❫ Instrumentational Concepts ○ ❪✺₁❫ Electrical Engineering Classes ○ ❪✺₁❫ Metrological Classes ○ Charge-Coupled Device (CCD) ○꠹ Gas Counter ○꠹ Proportional Counter ○꠹