You have a new test and you don't know how accurate it is. You have a new cholesterol test. You don't know how accurate it is. You know that in order for it to be approved by whatever governing body, it has to be accurate 99, the probability of it being accurate has to be 99%. So needs to have probability of accurate equal to 99%. You don't know if this is true. You just know that that's what it needs to be.