I am having a problem with  coordinate systems...
I create my wheel layer,  I stick it in the centre of the screen


-(id) init
{
    if( (self=[super init] )) {
        Wheel * wheel = [ [ [Wheel alloc] init] autorelease];

        [wheel setupWithMagnets: 3];

        // takes orientation into account
        CGSize winSize = [[CCDirector sharedDirector] winSizeInPixels];
        printf("%f, %f\n", (float) winSize.width, (float) winSize.height);

        wheel.position =  ccp ( winSize.width / 2 - 1, winSize.height / 2 - 1 );
        printf("%f, %f\n", (float) wheel.position.x, (float) wheel.position.y);


        [self addChild: wheel];

        // - - -

    }
    return self;
}



Now straightaway I don't understand why it positions itself correctly with the centre of the layer in the centre of the screen
 surely it would only do this if the wheel's  self.anchorPoint = ccp (.5, .5);
 but I never explicitly  set it,  and the default is 0,0

- (void) setupWithMagnets: (int) in_magnets
{
    self.magnets = in_magnets;

    self.magnetOffset = 0;

    //self.anchorPoint = ccp (.5, .5);

    CCLayerColor* colorLayer = [CCLayerColor layerWithColor: ccc4(0, 67, 67, 67)];
    colorLayer.anchorPoint = ccp (.5, .5); // << makes no diff
    [self addChild:colorLayer z: -1];

    thetaWheel = 0.;
    dTheta_dt = 0.;
    mass = K_WHEEL_MASS;
    tracking = NO;

    [self schedule: @selector(displayLinkIsCallingBack:)];


    [[CCTouchDispatcher sharedDispatcher] addTargetedDelegate: self
                                                     priority: 0
                                              swallowsTouches: YES];

    //displayLink = [CADisplayLink displayLinkWithTarget: self
    //                                        selector:
    //             @selector(displayLinkIsCallingBack:) ];

    //[displayLink addToRunLoop: [NSRunLoop currentRunLoop]
    //                forMode: NSDefaultRunLoopMode ];

    CCSprite * centerMarker = [CCSprite spriteWithFile: @"Icon.png"];
    centerMarker.anchorPoint = ccp (.5, .5);
    centerMarker.position = ccp(0, 0);
    [self addChild: centerMarker];

    for (int i=0; i<3; i++)
    {
        CCSprite * button = [CCSprite spriteWithFile: @"seeker.png"];

        float RADIUS = 150.;
        float theta = M_TWO_PI * (i / 3.) - M_PI / 2.;

        button.anchorPoint = ccp (.5, .5);
        button.position = fromPolar(RADIUS, theta);

        [self addChild: button];
    }
}


- (void) displayLinkIsCallingBack: (ccTime) deltaT
{
    // Display link fires every time the screen is to be refreshed
    // The wheel remembers its angle and its velocity
    // Each time display link fires, potentially TWO forces act upon the wheel

    // (1) When user initiated contact, fingerprint position on wheel was recorded
    //     as finger moves, invisible elastic stretches between finger and fingerprint,
    //     pulling wheel towards finger
BLA
    // (2) imagine a magnet sitting behind the centre of each button.
    //     These magnets encourage the wheel to settle exactly in
    //     one of its preset positions
BLA
    // using CATransaction like this goes from 14fps to 19fps
    //[CATransaction begin];
    //[CATransaction setDisableActions: YES];

    // NEG, as coord system is flipped/fucked
    //self.transform = CGAffineTransformMakeRotation(-thetaWheel);

#define FAC  (-360. / M_TWO_PI)

    self.rotation = FAC * (-thetaWheel);
    //[CATransaction commit];
}