digital bradley smoker temp accuracy

hello and thanks in advance     i have a newer DBS and id like to know if anyone knows what the temp diff is in the middle of smoker compared to the actual pid reading.    i cannot afford a digital probe just for monitoring cabinet temps  and i know you all will recommend one so my question is  on average if my pid reads 230   whats the real temp in the middle?    id like to adjust my oven temp setting to this offset.   it is prob the same for them all   im thinking plus or minus 25 deg guessing.   what have you guys seen?  higher or lower and by how much?