Tiny amount of magnetic resistance dealt with (9)
I believe the answer is:
centigram
'tiny amount' is the definition.
The definition suggests a singular noun which matches the answer.
'of magnetic resistance dealt with' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'resistance' becomes 'r' (abbreviation in physics and electronics).
'dealt with' is a charade indicator (letters next to each other) (some letters placed down or dealt alongside others).
'magnetic' after 'r' is 'rmagnetic'.
'rmagnetic' anagrammed gives 'CENTIGRAM'.
Can you help me to learn more?
(Other definitions for centigram that I've seen before include "small weight" , "Small mass" .)