A good hands on technique would be to use some of your own jewelry, whether yours or your wife if you are married, to see how the detector reacts to that. I am not schooled on the ace 250, but if it has numbers or tones to correspond to those different types of rings, then that will help you out. Also, depending on where he lost it, it will not be buried but rather at or near the surface so you don't need to crank up the sensitivity. I can't help you if it's made of something like platinum, but if its a silver ring then it will come in just like a silver coin like a quarter, maybe even a half or dollar sized depending on size of the ring. As long as you don't notch it out and get your coil over it, you should find it. The easy part is if its not right at the surface; if it calls for you to dig, then that is not his ring unless he lost it a long time ago. Good luck!