By numbers (7)
I believe the answer is:
digital
'by' is the definition.
Although both the answer and definition are adjectives, I cannot see how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for digital that I've seen before include "(Watch) without hands" , "Replacement for analogue" , "Like computer technology" , "Key" , "Opposite of analogue" .)