> 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, and it keeps CIZE reliable.**
See [Maintenance schedule](/maintenance/maintenance-schedule.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).
---
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