# Force distance

## Introduction

This module allows the user to measure force distance curves while moving a trap towards an absolute or relative
position.

## General settings

![](images/ForceDistance1.png)

The following settings are available:

- Trap: Which device will be moved (Trap 1, 2,.... or Nanostage)
- Speed: The speed of the movement
- Pause: The amount of time to pause after each movement (when there is more than one movement to be made, like in the
  case of ping-pong)

## Start position

![](images/ForceDistance2.png)

The starting position of the movement can be either an existing waypoint, or the current device position.

## End position

![](images/ForceDistance3.png)

The end position of the movement can be either an existing waypoint, or a position relative to the start position. It
can be set both as a delta `(X, Y)` from the starting point, or as a direction + magnitude using the starting point as
origin.

## Measurement

![](images/ForceDistance4.png)

_(for baseline correction measurements, see the [Force baseline correction section](baseline_correction_manual.md))_

The measurement can be done using the "To Start", "To End" and ping-pong buttons. It can be stopped at any time using
the stop icon. The behavior depends on the type of start and end positions selected:

### 1. [Start = Current position],  [End = Relative]

- **To Start:** move back (negative direction/reversing). Assuming there was a move command before, this will bring us
  back to the starting position.
- **To End:** move forward (positive direction) by the relative value.

### 2. [Start = Waypoint], [End = Relative]

- **To Start:** move to the waypoint, regardless of origin.
- **To End:** move from the waypoint by the relative value.

### 3. [Start = Waypoint 1], [End = Waypoint 2]

- **To Start:** move to Waypoint 1 regardless of starting position.
- **To End:** move from Waypoint 1 to Waypoint 2 (_if before this step the current position is not Waypoint 1, the first
  move is towards Waypoint 1 and then to Waypoint 2_)

### 4. [Start = Current position], [End = Waypoint]

- **To Start:** Not possible (button is disabled)
- **To End:** move to the waypoint, regardless of origin