If you are using a pump without a gauge, like a Bathmate, as you are fully erect while pumping, there is no sensation of your penis is being expanded. That can be anywhere between 3inHg to 4.5inHg (low pressure zone). When you start to feel your penis is being tugged or being forced to expand, that can range between 4inHg to 6inHg (moderate pressure zone). When you start to feel the pressure forcing the pennis to expand nearly reaching an uncomfortable feeling without tingling pain, you are at high pressure zone. Any more is dangerous for you at the moment. That high pressure zone can be anywhere between 5inHg to 8inHg. This is why it's critical to know your pressure at all time.