When it's past you
Some of them need a vet. It will tell you which.
An app that only gives you a percentage leaves you where it found you, at two in the morning, with your arm in a ewe. This one says when it's past what you should do alone, and gets a vet on the phone.
They pick up knowing the signs, how long, her temperature, what she's had. You don't spend five minutes explaining the last two hours.