# GDScript: Callback values

Source: https://tweens.gd/gdscript/nodes/values/

These target any `Node`, write no property, and deliver each sample to `on_update`. See [callback values](https://tweens.gd/gdscript/custom-properties/#callback-values).

| Helper | Value |
| --- | --- |
| `color_value` | Color |
| `double_value` | float |
| `float_value` | float |
| `quaternion_value` | Quaternion |
| `rect2_value` | Rect2 |
| `vector2_value` | Vector2 |
| `vector3_value` | Vector3 |
| `vector4_value` | Vector4 |

## Units and constraints

-   GDScript represents both `float` and `double` as `float`. `double_value` exists to match the C# catalog.
-   With no `from_value` or `to_value`, the definition uses zero, transparent black, or identity for that endpoint.