The most common and most likely answer to this crossword clue is the 8 letter word NOMOGRAM
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More clues leading to the result NOMOGRAM
Buddy explains!
The straight part
We know that "Mathematical chart" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mathematical chart = nomogram.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 NOMOGRAM mean?
NOMOGRAM noun- A diagram in which the relationship between three variables is represented by a straight line or curve for each variable; the value of the third variable corresponding to particular values of the first two is obtained by drawing a straight line through the points on the first two curves that represent particular values of the first two variables and noting the point at which the line intersects the third line or curve.