> ## Documentation Index
> Fetch the complete documentation index at: https://docs.navnx.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Measurements

> Using length and angle measurement tools in the planner.

## Measurement Tools

NavNX provides measurement tools for taking precise anatomical measurements on both 2D slices and the 3D bone model. Measurements are calibrated using the pixel spacing data embedded in the DICOM files.

## Bone 3D View

On the Bone 3D view, measurements are placed via the right-click context menu.

### Length (Distance)

<Steps>
  <Step title="Right-click on the bone surface">
    Right-click where you want to start the measurement. A context menu appears.
  </Step>

  <Step title="Select Measure distance">
    Click **Measure distance** from the menu. The first point is placed at the click location.
  </Step>

  <Step title="Left-click for the second point">
    A prompt appears: "Click on bone surface to place point 2/2". Left-click on the bone surface to complete the measurement. The distance is displayed in millimetres.
  </Step>
</Steps>

### Angle

<Steps>
  <Step title="Right-click on the bone surface">
    Right-click where you want to start the measurement.
  </Step>

  <Step title="Select Measure angle">
    Click **Measure angle** from the context menu. The first point is placed.
  </Step>

  <Step title="Left-click for two more points">
    Click the vertex (centre point), then the third point. The angle is displayed at the vertex in degrees.
  </Step>
</Steps>

### Camera Interaction

When you orbit, zoom, or pan the 3D view, the on-screen measurement markers (lines and labels) are automatically hidden. This is intentional — screen-space markers become misleading when the perspective changes.

Your measurement data is **not lost**. It remains visible in the properties panel sidebar and is saved with the case.

### Erasing Measurements

Right-click near a measurement and select **Erase nearest** to remove it. Alternatively, use the **Clear all** button in the measurement overlay or the × button next to each measurement in the sidebar.

## 2D Slice Views (Stack / MPR)

On 2D slice views, measurements are placed using the toolbar tools.

### Length Tool

<Steps>
  <Step title="Activate the tool">
    Click the **Length** button in the toolbar (ruler icon) or press **L**.
  </Step>

  <Step title="Place the first point">
    Click on the viewport to set the start point.
  </Step>

  <Step title="Place the second point">
    Click again to set the end point. The measurement is displayed immediately in millimetres.
  </Step>
</Steps>

### Angle Tool

<Steps>
  <Step title="Activate the tool">
    Click the **Angle** button in the toolbar (protractor icon) or press **A**.
  </Step>

  <Step title="Place three points">
    Click to set the first point, then the vertex (centre), then the third point. The angle is displayed at the vertex.
  </Step>
</Steps>

## Annotations

Each measurement can be annotated with a label (e.g. "PCL entry to plateau"):

* In the **sidebar**, type in the label field below each measurement
* On the **3D overlay**, click the ✎ icon next to a measurement

## Persistence

Measurements are saved as part of the case plan. They persist across:

* Switching between view modes
* Closing and reopening the case
* Camera changes on the 3D view (data preserved, markers refresh)

<Note>
  Measurements are included in the pre-op report when you print or export it.
</Note>