Yep, another case of factory installed thermometers not being calibrated. You can calibrate most any dial thermometer...there should be a hex on the stem next to the dial case (most of mine fit a 7/16" end wrench), inside the cook chamber. The exception being a button-type temp sensing dial like on some cheaper pit/grill combos...they're non-adjustable.
If it makes you feel any better, most will tell you their brand new smoker thermometer is way off...50 to 100+*F...I've never had one that was very close right out of the box...Weber kettle, Smokey Mountain GOSM, Smoke Vault, oven/deep fryer/accessory thermometers...the list goes on. It's best to check your cooker factory thermometers when you season them...verify with a digital probe or other thermometer (that you have personally biol-tested) placed close to the factory thermometer's stem/base. Even if you don't know how or can't make adjustments you will have a baseline reading for reference. I like to recheck mine after transporting and at least once a year, or more often as dictated by subsequent accuracy checks.
Eric