I checked mine and it was spot on.  Of course that was years ago... it could be off now but I still use it.  In fact, I rarely use the Mav or iGrill anymore.  I simply set it up the grill or smoker the way I always do for a particular cook and glance at the thermo from time to time.  When I figure cookin is close I start checking with a thermopen or skewer depending on the critter I am cooking.