# Buttons
## The four buttons: MeasureStopEmptyClean
BactoBox® has four buttons on the top side:
Measure (C), Stop (D), Empty (E), and Clean (F)
### Start program
When you press Measure, Empty, or Clean, BactoBox® starts the corresponding program.
{% hint style="info" %}
**BactoBox® helps you avoid common mistakes**
For example, if you press Clean but there is no flow cell in the device, BactoBox® does nothing. This avoids leaks.
Likewise, if it has been a long time since the last clean, BactoBox® may block the *Measure* program until you run *Clean*. This reduces instrument background when you measure your samples.
{% endhint %}
#### The Empty button
If BactoBox® stops unexpectedly during a measurement, it still has liquid inside. Use the Empty button to drain the liquid from the flow paths into the vial.
{% hint style="success" %}
### You rarely need to press the Empty button
The Empty button is only there for special cases. E.g., if the power goes or if an error occurs.
If BactoBox® detects liquid inside, it prompts you to press Empty. You don't even need to remember this yourself, BactoBox® helps you out. BactoBox® even remembers this across a power off.
{% endhint %}
### Stop program
When you press the Stop button, BactoBox® immediately stops the current program. If there is liquid in the flow paths, BactoBox® empties the flow paths first.
{% hint style="success" %}
### Give it time to empty the flow paths
Leave the tubing kit in the vial until the *emptying* phase is done. This ensures that *all* liquid goes back into the vial.
{% endhint %}
## Navigation mode: OK←∨∧
Certain screens in the [user interface](/encyclopedia/software/user-interface.md) require additional input. E.g., to navigate the [menu](/encyclopedia/software/user-interface/menu-system.md) or to set the time and date. For this purpose, BactoBox® automatically remaps the buttons to *navigation mode*. When there is a OK←∨∧ bar in the bottom of the screen, you know that the buttons are in navigation mode:
BactoBox® is in navigation mode when you enter the menu. Notice the OK←∨∧ bar in the bottom.
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