Simplest most effective method IMO...
Buy a few tubes of cheap, pop-open biscuits.
Get smoker up to temp.
Place raw biscuit dough on each corner, in the middle, etc of each rack.
After 15-20 minutes (or more) open it up and look at your biscuits. The darkest ones are your hot spots, lightest ones your cooler spots, etc. Easy visual indicator of what's happening in your smoker, top to bottom, side to side, temp wise.
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