> 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/everyday-use/before-you-measure.md).
# Before you measure
The five mistakes we see most often, and how to avoid them.
Most of these mistakes give you a wrong number that looks right. Read the linked page for each one before your first sample.
## 1. Vortex and pipette properly
Vortex until a tornado-like funnel forms in the liquid. If the surface only trembles, keep going. When you pipette small volumes, rinse the tip so no cells stay behind.
**A mistake here gives a high coefficient of variation (CV) in your results.**
See [Basic sample preparation](/more/how-to-guides/basic-sample-preparation.md).
## 2. Clean every time, deep clean every week
Run Clean after every measurement. Once a week, run Deep clean (15 minutes) and a QC test.
**Cleaning prevents carry-over from one sample to the next. The QC test is how you know your setup still performs well.**
See [Maintenance](/everyday-use/maintenance.md).
## 3. Know if your organism clumps
Some organisms form chains or clumps that a vortex cannot separate, and your BactoBox® counts each one as a single cell. If yours does, break them up before you measure.
**A clumped sample reads low.**
See [Break up cell clumps](/more/how-to-guides/break-up-cell-clumps.md).
## 4. Check your medium for background
Some media contain many particles. At low dilutions, such as 1:100, a few may be counted as cells.
**Background makes your count read high.**
See [Check medium background](/more/how-to-guides/check-medium-background.md).
## 5. Know what cells/mL means
Cells/mL is a direct count of whole cells in the sample you diluted. It is not CFU, and it is not OD. It tracks CFU closely while cells grow.
**Keep this in mind when you interpret your data and decide what to do next.**
See [BacTotal-10](/advanced/measurements-explained/gating/bactotal-10.md).
---
# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.
## 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, and the optional `goal` query parameter:
```
GET https://help.sbtinstruments.com/everyday-use/before-you-measure.md?ask=&goal=
```
`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.
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.