Bests & Worsts Reviews from Amazon

I'm a temperature nerd. I have multiple little devices like this (various brands) throughout the house. I know with cheap little units like this you can't expect pinpoint accuracy, but I bought this one based on it's high rating and the fact that many reviewers were commenting on it's accuracy. I think I may have gotten a bum unit because the outside readings keeping cutting in and out. I've tried resetting it, different channels, taking the batteries out, etc and the reading won't stay steady. It will show a reading and then lines will just appear across the outside temp and humidity areas. Also, even when it's reading the outside temp, it never shows the outside humidity. Mine just says "LL". The instruction manual doesn't explain what this means. Regarding the accuracy, as I said, I have various temp gauges and thermometers inside and outside the house. The inside readings are consistent with my other gauges, but the outside temp is consistently 5-10 degrees higher than my other digital gauges, the mercury thermometers, and a weather station 1 mile away from my house. I'll contact the seller to see about a replacement and if they send one and it works, I'll revise this.