> For the complete documentation index, see [llms.txt](https://help.sbtinstruments.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.sbtinstruments.com/advanced/measurements-explained/limits-of-detection.md).
# Limit of detection
BactoBox® counts individual particles. If there are too *few* particles, the concentration estimate is too uncertain. If there are too *many* particles, we can't tell them apart. Therefore, we have limit of detection (LoD). BactoBox® outputs concentrations in these ranges:
* 30 000–5 000 000 **cells/mL** (3·10⁴ to 5·10⁵ cells/mL)
* 30 000–5 000 000 **total/mL** (3·10⁴ to 5·10⁵ total/mL)
{% hint style="success" %}
## Target 0.5–4 million cells/mL for fast results
The more things to count, the faster we are certain about the concentration. Give BactoBox® something to work with and it triggers the *Fast results* feature :fast\_forward:.
Make a dilution series and [**measure the most diluted sample first**](/advanced/advanced-sample-preparation/hit-the-right-concentration/dilute-1-100.md#measure-the-most-diluted-sample-first). Aim for 0.5–4 million cells/mL.
{% endhint %}
The figure below shows how the LoD influences the BactoBox® output. The figure uses *total/mL* as an example but the very same thing is true for *cells/mL*.
{% hint style="info" %}
## Don't know the concentration of your sample?
Make a dilution series and [**measure the most diluted sample first**](/advanced/advanced-sample-preparation/hit-the-right-concentration/dilute-1-100.md#measure-the-most-diluted-sample-first). This avoids clogging your BactoBox® setup. It also avoids carry-over from your previous sample vial.
Once you are above the lower limit of detection (30 000 cells/mL), target 0.5–4 million cells/mL.
{% endhint %}
## Above the upper limit
Cross the upper limit and BactoBox® can no longer tell the particles apart, so it stops with an error instead of a result. A concentration above 5 000 000 particles/ml also risks clogging the flow cell.
Above the upper limit, BactoBox® shows Error 3000 instead of a result.
Discard the sample, clean the device, and measure again at a higher dilution.
## Single cell at a time
The following figure shows how both too *few* and too *many* cells cause trouble.
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