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PID (Proportional Integral Derivative) is the control algorithm the printers use for holding temperature. The parameters for this algorithm control how fast the printer reaches the set temperature and how well it holds that temperature once it gets there.
how to:
Connect to your printer via Octoprint / Prontoface.
In the terminal send:
M303 E0 S220 C8 “enter”
M303 is the code for Pid-auto tune / E0 is your hotend - S220 is the temp you want to calibrate for - C8 is the number of passes (here its 8)
Now let it run-
After its done the terminal will give you your new KP-KI-KD values.
In my case :

Recv: // Kp: 15.926294 Ki:1.020720 Kd:62.124493
Recv: //PID Autotune finished!
Recv: ok N:202
Now to set the new PID
In the terminal type:
M301 P15.926294 I1.020720 D62.124493 (Use your own KP - KI -KD values)
Check its set by entering:
M301
Finish by saving
M8500 (here Octoprint writes some errors and your printer beeps) ***
But your new PID has been savend to the eeprom.
Now reboot your printer and have fun printing
***The M8500 is used to save on Chitu boards, if you are running Marlin the save code is M500