DOMBETT  Yeah, basic biology says that if you have sex within the 6 days of ovulation you have a chance of getting pregnant so that's how they determine that timing. That's obviously not a guarantee; more like a broad range of abstinence.

But take what the developers themselves say about the product. They're not marketing it as birth control despite the "avoid pregnancy" warning. So dinging them as ineffective birth control seems off target.  
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DOMBETT  Since the developer said the app was intended to help someone get pregnant, criticizing it as a bad form of birth control seems to miss the point.

While it's no substitute for other more scientifically accurate methods of determining fertility, I can see this being an aid for the couple who do not have any known physical problems getting pregnant but just want to keep track of the woman's cycles.  
(Version 1.0.1)