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## How to determine the biasing electrode position

To get 20 mm displacement one needs to do 20 full rotations.

For simplicity one can estimate the distance of the biasing probe from the center of the chamber as the number on ruler __a__.

| measurement  |  *a* [mm]  |  *b* [mm]  | *c* [mm]|
|-------|-------|-------|-----|
|   1  |   48  |  85  |  238  |
|   2  |   28  |  105  |  218  |


One can see where the dimensions *a*, *b* and *c* were measured on the following figure:
![alt text](http://golem.fjfi.cvut.cz/wiki/Infrastructure/Tools/BiasingElectrode/OldCastor/Logbook/0519FilipP/vyznacene_udaje.jpg)