In 2025, the PGA Tour began a six-week trial of using rangefinders, or distance-measuring devices (DMD), at specific tournaments. This week at the CJ Cup Byron Nelson event in McKinney, Texas, marks the third week of the experiment.Unfortunately for PGA Tour pro Davis Riley, he learned to double-check the settings as he became the first to receive a penalty with the new rule.He called a two-stroke penalty on himself for using the slope feature on the range finder while he played the 17th hole, his eighth hole of the day."Without thinking anything of it, I whip the Bushnell out of the bag, and then shoot it. It pops up a second number there with the adjusted number," Riley explained. "In that moment, I was just like, 'Wow,' it's one of those times that it sucks. It was a tough deal, and it's a bad break."While players can use the distance measuring device, they cannot use its slope aspect.Riley hit his tee shot to 12 feet and made par, but after the penalty, he settled for a double-bogey. Rules official Ken Tackett confirmed the situation and agreed that the two-time PGA Tour winner made a five on that hole.After that happened, Riley began to let the situation affect him."I looked at my caddie and told him, 'Man, I'm struggling. I'm angry,'" he said. "My head's spinning because I'm right around the cut and I'm playing good and want to make a move, but then you kind of take a punch on 17."Riley leaned on his caddie, David Streza, for the remaining 11 holes as he fought to make the cut."I told my caddie, 'Hey, man, I need you... just guide me around because my head's spinning a little bit.' He did a good job of that, and I hung in there and played okay coming in," Riley noted.The penalty put him outside the cut line, but Riley made an eagle from 11 feet, 3 inches on his 36th hole (the par-5 9th) to get to 5-under overall.He made the cut right on the number, so it seems the golf gods rewarded him for self-reporting his mistake.What are your thoughts on using rangefinders during PGA Tour events? Let us know in the comments.More Golf: OWGR Refutes Reports of LIV Golf Inching Closer to Earning Points