2 different baby heart rate readings?

Ok, so I was using my doppler at home, and I was searching for baby. I kept hearing "me" at 82, 80, 79, 81 etc. Then I caught a faint baby heart rate and it read 183. My husband walks in and says he wants to try, so he puts the toggle about 5inches over and (less than a minute after my reading) finds a baby heart rate of 154. I'm trying to do math in my head and I can't figure out where the 183 came from. If baby and me were heard together wouldn't it read 200 something? Baby's bpm wouldn't jump that drastically would it?