### Customizing the chord grid style

Custom divisions of chord squares can be defined through the `measure-division-lines-alist` and `measure-division-chord-placement-alist` properties of `ChordSquare`. These are both alists. Their keys are measure divisions, namely lists which give the fraction of the measure that each chord (or rest, or skip) represents. More precisely, a measure division alist is made of positive, exact numbers adding up to 1, for example: `'(1/2 1/4 1/4)`. The exactness requirement means that, e.g., `1/2` is valid but not `0.5`.

The values in `measure-division-lines-alist` are lists of lines, which are represented as `(x1 y1 x2 y2)`. The line starts at the point `(x1 . y1)` and ends at `(x2 . y2)`. Coordinates are expressed in the [-1, 1] scale relative to the extent of the square.

The values in `measure-division-chord-placement-alist` are lists of `(x . y)` pairs giving the placement of the respective chords.

This example defines a peculiar chord grid style that has a rule for measures divided in three equal parts.

```\paper {
line-width = 10\cm
ragged-right = ##f
}

\new ChordGrid \with {
\override ChordSquare.measure-division-lines-alist =
#'(((1) . ())
((1/3 1/3 1/3) . ((-1 -0.4 0 1) (0 -1 1 0.4))))
\override ChordSquare.measure-division-chord-placement-alist =
#'(((1) . ((0 . 0)))
((1/3 1/3 1/3) . ((-0.7 . 0.5) (0 . 0) (0.7 . -0.5))))
}
\chordmode {
\time 3/4
c2.
c4 c4 c4
}
```