Crossword Genius

Resistance units (4)

Ross

I believe the answer is:

ohms

'resistance units' is the definition.
(ohm is a kind of resistance unit)

This is the entire clue.

(Other definitions for ohms that I've seen before include "Frank on official post" , "Electricity" , "measures of resistance" , "Frank marking" , "Letters with official status in correspondence" .)

I've seen this clue in The Times, the King Feature Syndicate, the New York Times and the Universal.
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