iPhone Accelerometer calibration

Question

How do I properly calibrate the accelerometer for my iPhone game? Currently, when the phone is on a flat surface, the paddle drifts to the left. High or Low Pass filters are not an acceptable solution as I need complete control over the paddle even at low & high values. I know Apple has the BubbleLevel sample but I find it difficult to follow... could someone simplify the process?

My accelerometer code looks like this:

-(void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {

float acelx = -acceleration.y;
float x = acelx*40;

Board *board = [Board sharedBoard];
AtlasSprite *paddle = (AtlasSprite *)[board.spriteManager getChildByTag:10];

if ( paddle.position.x > 0 && paddle.position.x < 480) {
    paddle.position = ccp(paddle.position.x+x, paddle.position.y);
}

if ( paddle.position.x < 55 ) {
    paddle.position = ccp(56, paddle.position.y);
}

if ( paddle.position.x > 435 ) {
    paddle.position = ccp(434, paddle.position.y);
}

if ( paddle.position.x < 55 && x > 1 ) {
    paddle.position = ccp(paddle.position.x+x, paddle.position.y);
}

if ( paddle.position.x > 435 && x < 0) {
    paddle.position = ccp(paddle.position.x+x, paddle.position.y);
}
}

Thank you!

Answer 1

Okay, problem SOLVED and the solution is so simple I'm actually embarrassed I didn't come up with it sooner. It's as simple as this:

In a "Calibration Button":

//store the current offset for a "neutral" position
calibration = -currentAccelX * accelerationFactor;

In the game time accelerometer function:

//add the offset to the accel value
float acelx = -acceleration.y;
float x = (acelx * accelerationFactor) + calibration;

It's as simple as adding the offset. * hides his head *