Before you assemble the bottle and attach the nipple to the ring (collar), and prior to each feeding
Flip the nipple upside down, find the slit on the tiny semi-circle at the nipple base, and squeeze the outside edges until the slit opens briefly. Then assemble the bottle. It is not necessary to line the vent up with the cap-ring notch or point it toward the baby's nose.
Slow Flow (0 Months+)
Use the included Slow Flow nipple. On Balance + nipples, the flow marking is S.
Medium Flow (3 Months+), or if baby starts fussing with the bottle, unlatches and re-latches throughout the feed, collapses the nipple during a feeding, acts agitated, bites or tugs on the nipple, sucks several times before swallowing, takes longer to feed than previously, or leaves milk in the bottle
Switch to the next flow rate and see if feedings go back to normal. For this product line, the next flow after Slow is Medium Flow; the nipple marking is M.
Fast/X-Cut Flow (8 Months+), or if you see the above feeding behaviors again a few months down the road
Try the next flow rate again if the same move-up signs return later. For this product line, the next flow after Medium is Fast/X-Cut Flow; the nipple marking is X.