get better EXT0_STEPS_PER_MM value

Hi. i'm trying to get better extruder calibration, but the changes i do on firmware (customizing EXT0_STEPS_PER_MM value on configuration.h) do nothing.

Just now, when i open host software and execute "extrude 10mm of PLA at 200 temp" i think i get a bit more plastic extruded.

I was following
[richrap.blogspot.ca]

so i used to mark 30mm with a pencil on PLA filament, and extrude 2 times 10mm each (or 4*5mm, i have change this with same results) and i expected take the exact amount on filament really extruded, and calibrate the extruder progressively.

But when i change the EXT0_STEPS_PER_MM (i did it the same with EXT1_STEPS_PER_MM) to the 373 initial value to (for example) 266, and 183....when i repeat the proof on hosting software i get exactly the same distance of filament been extruded when i exec "2 times 10 mm each"...

Any clue?
Thanks.

Which firmware are you using? Looks like it's Sprinter or Marlin. Values in configuration.h might be ignored in favour of values set by G-code commands. See M82 & friends.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

i am using Repetier firmware 0.71.
I changed configuration.h included on directory

"..\repetier-firmware-0_71\Repetier"

So i can not understand the reason that Repetier-Host software is sending G-code commands that firmware did not recognize!!

Anyway, how could i do to change/calibrate the extrusion param STEPS_PER_MM with Repetier firmware?

The value is probably also stored in EEPROM. Find the EEPROM settings in your RepetierHost (second menu from the left, I believe),
and try changing it there.