When pressing the bottom half of the pusher, you split the minute hand. In the top photo you will see a black hand with yellow lume pointing to about the 23 minute mark. This is usually hidden underneath the normal minute hand. When you press the button, the hand beneath locks into place and the top minute hand travels away from it. The time between the two hands is the time elapsed. Pressing the top half of the button will return the underneath hand perfectly under the minute hand, much like a rattrapante.