Portion of the code that does the deceleration

CustomScrollView.m

//get velocity from pan gesture
CGPoint velocity = [panGestureRecognizer velocityInView:self];
if (self.bounds.size.width >= self.contentSize.width) {
    //make movement zero along x if no horizontal scrolling
    velocity.x = 0; 
}
if (self.bounds.size.height >= self.contentSize.height) {
    //make movement zero along y if no vertical scrolling
    velocity.y = 0; 
}

//we need the negative velocity of what we get from the pan gesture, so flip the signs
velocity.x = -velocity.x;
velocity.y = -velocity.y;

POPDecayAnimation *decayAnimation = [POPDecayAnimation animationWithPropertyNamed:kPOPViewBounds];

//last two components zero as we do not want to change bound's size
decayAnimation.velocity = [NSValue valueWithCGRect:CGRectMake(velocity.x, velocity.y, 0, 0)];

[self pop_addAnimation:decayAnimation forKey:@"decelerate"];