The most common and most likely answer to this crossword clue is the 21 letter word ARBAORDSBOARDS/ARROBA
A
R
B
A
O
R
D
S
B
O
A
R
D
S
/
A
R
R
O
B
A
Buddy explains!
The straight part
We know that "Stage/variable weight" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stage/variable weight = arbaordsboards/arroba.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.