In certain charts it may indicate a mile (4)
I believe the answer is:
inch
'it may indicate a mile' is the definition.
The definition suggests a singular noun which matches the answer.
'in certain charts' is the wordplay.
'in' says the answer is hidden in the clue.
'INCH' is hidden within 'certain charts'.
Can you help me to learn more?
(Other definitions for inch that I've seen before include "Crawl; imperial measurement" , "Edge (forwards)" , "Imperial unit of length" , "Edge towards" , "0.0254 metre" .)