Because the probes that came with the unit, I could not clearly see the “ring” where you insert them into the meat. Now my probes won’t recharge. I bought one for my son and he used it and likes it. His are recharging fine. When I told him about my problem he sent me a picture of one of his probes and his has the circle in black which can clearly be seen. So I believe there's been a change in the design because people were having the same problem I was. I hope I receive a set of new probes for free with the circle in black which can be clearly seen.