The PSE button will pause the scan when in search mode so you can stop the scanner on a freq when you find something you want to listen to. The PSE also works to pause on a talk group when scanning a trunked system. The Tune button will allow you manually tune up or down using the arrows when you are in PSE mode. I.e. if you pause on a freq and it is not clear you can hit tune which will put the scanner in fine tune mode and by pushing the up arrow or down arrow you can step up or down to the next freq.