# Units

Each TunnelCAD project stores its own unit settings, controlling how angles, coordinates, and stations are displayed throughout the application. Configure units via **File > Settings... > Units**.

## Angular units

TunnelCAD supports four angular unit systems:

| Unit | Display example | Description |
|---|---|---|
| Degrees | `45.0000` followed by degree symbol | Decimal degrees |
| DMS | `45`deg`00'00.0000"` | Degrees, minutes, seconds |
| Gradians | `50.0000g` | Gradians (gon), where 400 gon = 360 degrees |
| Radians | `0.7854 rad` | Radians |

The default angular unit is **Gradians**.

```{admonition} Note
:class: note
All angles are stored internally in radians regardless of the display unit. The angular unit setting only affects how values are presented in the interface.
```

## Station format

Chainages (stations) can be displayed in two formats:

| Format | Example | Grouping |
|---|---|---|
| `0+000` | `1+250.000` | Groups of 1000 |
| `00+00` | `12+50.000` | Groups of 100 |

The default station format is `0+000`.

## Decimal places

Separate decimal-place settings control the precision of displayed values in different contexts. All values range from 0 to 6 decimal places:

| Setting | Default | Applies to |
|---|---|---|
| Coordinates | 3 | Northing and Easting values |
| Elevations | 3 | Height / elevation values |
| Angles | 4 | Angle and bearing displays |
| Stations | 3 | Chainage / station values |
| Offsets | 3 | Lateral offset values |

## Coordinate system

TunnelCAD uses a standard surveying coordinate system:

- **Northing (Y)** -- north-south position, increasing northward.
- **Easting (X)** -- east-west position, increasing eastward.
- **Elevation (Z)** -- vertical position, increasing upward.

## Offset convention

Cross-section offsets are measured laterally from the alignment axis:

- **Positive (+)** values are to the **right** of the alignment direction.
- **Negative (-)** values are to the **left** of the alignment direction.

This convention applies to both setout offsets and measured offsets in cross-section data.

## Bearings

Bearings are displayed as surveying bearings measured clockwise from north. Internally, angles are stored as mathematical angles (measured counter-clockwise from east). The conversion is performed automatically:

> Bearing = 90 degrees - mathematical angle

Bearings are formatted using the project's angular unit and angle decimal-place settings.

## Gradient

Gradient values are stored and displayed directly in percent (%). A gradient of `2.5` means a 2.5% slope. The values are not multiplied by 100 for display -- they are already in the correct unit.