Dimmer student finally admitted to county town after pretty low grade (3,6)

I believe the answer is:

dip switch

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But I can't explain it at all! Could you help me understand?

(Other definitions for dip switch that I've seen before include "control of car" , "Uses ducking-stool, perhaps" , "way to reduce glaring" , "Electrical device" , "with which one lowers beam" .)

I've seen this clue in The Guardian.

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