Larry is right. If you have 3 holes and block one, 1/3 is blocked! :P
I use a weber el cheapo therm that is placed through a toggle bolt "nut" that allows smoke to go through every hole in the top vent. Did that with my first WSM cook just because it kept the dial from smothering the hole. Thought about the cork deal, but like Larry I didnt want the air flow to stop.
I bought that cheap thermometer about 2 years ago and it reads dead on.
I use a weber el cheapo therm that is placed through a toggle bolt "nut" that allows smoke to go through every hole in the top vent. Did that with my first WSM cook just because it kept the dial from smothering the hole. Thought about the cork deal, but like Larry I didnt want the air flow to stop.
I bought that cheap thermometer about 2 years ago and it reads dead on.