Daily results swing on their own, even when nothing changes. Run one ad for 30 days without touching it and see how much is just noise.
d20
tap it to roll a click
A 5% conversion rate = a 20‑sided die
Conversion rate5%
1%2%3%4%5%
Daily ad budget (at $1 a click)
Your 30 days
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changes made to the ad: 0
sales each dayaveragenormal variance range (99.7% of days)
How is the normal variance range calculated?
It's the range a day's sales land in 99.7% of the time when nothing about the ad changes. That's the same idea as "within 3 standard deviations of the average." We calculate it from the exact odds of each click converting (the binomial distribution), so it stays accurate for small accounts, where the usual standard-deviation shortcut breaks down.