# Linearity

If your sample vial follows the [requirements](https://help.sbtinstruments.com/encyclopedia/measurements-explained/what-can-i-measure-on), you get great linearity and low variance.

{% hint style="warning" %}

## Sample vial requirements

Proper output requires proper input. Make sure that your sample vial follows the requirements. See [what-can-i-measure-on](https://help.sbtinstruments.com/encyclopedia/measurements-explained/what-can-i-measure-on "mention") and [prepare-your-sample](https://help.sbtinstruments.com/protocols/prepare-your-sample "mention").
{% endhint %}

{% hint style="success" %}

## Disaggregate your cells

Some cells tend to form clumps (aggregates), which makes them too big to measure with BactoBox®. Use [3 mm glass beads and a vortex mixer](https://help.sbtinstruments.com/protocols/prepare-your-sample/break-up-clumps-and-chains/disaggregate-mechanically#vortex-with-glass-beads) to disaggregate the cells in your sample vial.

**BactoBox® does *****not***** count particles outside the 0.5–5 µm range.**

See [break-up-clumps-and-chains](https://help.sbtinstruments.com/protocols/prepare-your-sample/break-up-clumps-and-chains "mention") for other disaggregation methods.
{% endhint %}

## Linearity

For [active cultures](https://help.sbtinstruments.com/encyclopedia/measurements-explained/broken-reference), BactoBox® shows great linearity between:

* BactoBox® cells/mL and the dilution factor
* BactoBox® cells/mL and plate counts (CFUs/mL)

This linearity covers the entire range given by the [limits of detection](#limits-of-detection-lod).

The table below shows how BactoBox® performs across various particle types. Note that all R<sup>2</sup> values are very close to 1, which indicates strong linearity across the tested range.

<table><thead><tr><th width="146">Particle type</th><th width="177" align="right">Tested range (1/mL)</th><th>Linearity with dilution factor</th><th>Linearity with plate counts</th></tr></thead><tbody><tr><td><em>Staphyloccus epidermidis</em></td><td align="right">30 000–5 000 000</td><td>R<sup>2</sup>=0.9975</td><td>R<sup>2</sup>=0.9982</td></tr><tr><td>1 µm silica microspheres</td><td align="right">1 000 000–5 000 000</td><td>R<sup>2</sup>=0.9995</td><td>N/A</td></tr></tbody></table>

The below figure illustrates the linearity for the *Staphylococcus epidermidis* linearity-response test.&#x20;

<figure><img src="https://4216107837-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FeYTtd7c0A325muFr5lMW%2Fuploads%2FGtj0tFfYdX3UrBjx2sSu%2FStaphEpi%20linearity%20DF.png?alt=media&#x26;token=9022f8c9-f31a-4b2a-8e44-0df90def018d" alt=""><figcaption><p><em>S. epidermidis</em> linearity response. Concentration of cells for the same primary sample measured at different dilution factors. Each data point represents arithmetic mean of technical triplicates. Error bars represent standard deviation.</p></figcaption></figure>


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://help.sbtinstruments.com/encyclopedia/measurements-explained/linearity-and-correlation.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.