# Electrostatic simulation- getting a field value
**URL:** https://community.freefem.org/t/electrostatic-simulation-getting-a-field-value/1500
**Category:** General Discussion
**Created:** [February 16, 2022, 9:21am UTC](https://community.freefem.org/t/electrostatic-simulation-getting-a-field-value/1500 "2022-02-16T09:21:47Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@maya2708](https://community.freefem.org/u/maya2708)
#### Post date: [February 16, 2022, 9:21am UTC](https://community.freefem.org/t/electrostatic-simulation-getting-a-field-value/1500/1 "2022-02-16T09:21:47Z")
Dear FF users and developers,
I have a general question regarding Free FEM software. To be clear, I have no experience with Free FEM. I’ve read FF user manual and a few tutrorials, but I did not manage to find the answers to my questions.
What I need to do create and solve 2D model representig the geometry around transformer windings (combination of bare/ paper insulated electrodes, insulating elements and transformer oil as liquid dielectric). For the purpose of post-processing I need to calculate („draw“) electric field streamlines in oil (between insulating elements). To do so, I need to get a field value (Ex, Ey) as well as dielectric constant (relative permittivity) at a certain point (x,y).
1. Can Free FEM do that- extract el. field values (Ex, Ey) and relative permittivity at predefined points?
2. Will domain with several regions (10-20) of different permittivty (dielectric constant) be a problem for Free Fem? Will it be complicated to write a function for permittivity?
The questions may be stupid, but answering them would save me a lot of time😊
Thanks in advance.
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### Author:  [@frederichecht](https://community.freefem.org/u/frederichecht)
#### Post date: [February 17, 2022, 1:01pm UTC](https://community.freefem.org/t/electrostatic-simulation-getting-a-field-value/1500/2 "2022-02-17T13:01:57Z")
It is not so difficult to choose or change the numbering of the region in FreeFEM with the
“change” function.
After it is write simple so cha7nge value for a region number;
real [int] Perm=[1,2,3,4,5,6,7,8]; // 8 go region form 0 to 7.
and in formulation use
perm[region] ( this is equal (region+1) ) the the formulation.