With a mum suction strength of 350mmHg and the ability to be used as a single or double pump, plus a host of additional features, the S1, like her sister the S2, is set to become the ultimate breast pump to support U.S. moms. Completely flexible, touch button with the S1 pump's digital controls. These allow you to set the pumping program to the speed and rhythm most effective for your body. The pump will start in 'massage mode', a short, shallow mode designed to stimulate your body's letdown reflex (start the milk flowing) just like how your baby tells your body to start milk flow. The pump will then switch to expression mode, a deeper, slower pattern of suction which mimics how your baby nurses when the milk is flowing. For women who find it hard to get a letdown when pumping, this feature really helps - switch back and forth as needed. The suction is also adjustable whether in let-down or expression mode. Includes a timer and nightlight. You can see on the picture that you can adjust both cycle (how often the pump 'sucks') and vacuum (the strength of the suction) easily, and the digital display allows you to see your program at a glance. Can be used with it's inbuilt battery for 1 hour on full charge or plug it in...it's up to you.