Pope Barbed Crosses

Pressure compensated driplines start dripping once the line has reached a specific level of pressure. It will then irrigate at that pressure across the entire line regardless of factors like elevation. That's what makes them best for drip irrigation that occurs across hills or slopes to make sure both the crops at the top and bottom of said slopes get the same amount of water.

Non pressure compensated driplines on the other hand would give more water to the drippers at the bottom of the hill due to gravity, which can result in uneven distribution of water. However, these are fine to use on flat surfaces.