The most common and most likely answer to this crossword clue is the 9 letter word STOCKTAKE
I've seen this crossword clue in Financial Times
S
T
O
C
K
T
A
K
E
Buddy explains!
The straight part
We know that "Count firm implements periodically" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case count firm implements periodically = stocktake.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 STOCKTAKE mean?
STOCKTAKE noun- The process of making an inventory of stock in a store or other location.
- The act or process of taking stock of something, or the result of that assessment.