Controlling Animation with CAAnimation - iOS Programming: The Big Nerd Ranch Guide - page 639

Spinning with CABasicAnimation
In this section, you are going to use an animation object to spin the implicit layer of the
time field in HypnoTime 's TimeViewController whenever it is updated ( Figure 23.5 ).
(Recall that an implicit layer is a layer created by a view when the view is instantiated. The
time field is a UILabel , which is a subclass of UIView , so it has an implicit layer that
we can animate.)
Figure 23.5 Current time mid-spin
Open HypnoTime.xcodeproj .