PID control loops - closed loop feedback

[Salik Syed]

degree seconds? i thought it would give the degree angle of the arm ...like a potentiometer... (degree/seconds * seconds = degrees ) right?



btw this is the actual code it hasn't been compiled or tested yet just theory...just notepad:

p2_y=armin;
targetv=armin;   //just temporary...

//////get gyro input conv to 8bit

(int)gyroin10bit=Get_Analog_Value(rc_anlg_in01);
gyroval=gyroin10bit/4;

////convert gyro values to usable values....
armaccel=gyroval-127;


///integrate
realv=(armaccel+realv)/time; 
time++;
//////////////



if((hicutoff+targetv)>realv>(locutoff+targetv))
	{
	armout=(targetv-realv)/proportion;
	}
pwm03=pwm03+armout;

One more thing... What is this about integral and derivative.... I get the proportional part (basically multiplying by how much change the input produces.."Gain" )
but why integrate the error....i don't get this and how it works ? i read some stuff about how it is an automatic reset which doesn't quite make sense to me...... Also can someone explain the derivative...part...