# `GSLayer axisInternalValueValue(forId:)`

*Instance Method*

Internal value for an axis, or `nil` when the axis is unknown.

## Declaration

```swift
func axisInternalValueValue(forId axisId: String) -> CGFloat?
```

## See Also

### Variation Axes

- [`GSLayer axes`](/Core/GlyphsCore/GSLayer/axes) — Axes used to locate the layer in its design space.
- [`GSLayer rule:matchesCoordinates:`](/Core/GlyphsCore/GSLayer/rule:matchesCoordinates:) — Whether axis values satisfy all bounds in a set of Alternative-layer rules.