The most common and most likely answer to this crossword clue is the 9 letter word UNDERFLOW
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Buddy explains!
The straight part
We know that "when value is too small to be shown" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when value is too small to be shown = underflow.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNDERFLOW mean?
UNDERFLOW noun- A current flowing below the surface.
- A condition in which the value of a computed quantity is smaller than the smallest non-zero value that can be physically stored; usually treated as an error condition
- The error condition that results from an attempt to retrieve an item from an empty stack
- To trigger the condition in which the value of a computed quantity is smaller than the smallest non-zero value that can be physically stored.