Then you can weigh arbitrary objects using your phone! Be careful, don't break your phone (don't try to stand on it to weigh yourself!)
I have a Melitta funnel for making single servings of coffee, but when I'm using it I can't see how full my mug is without lifting up, and they are mostly opaque, and the funnel doesn't hold a full mug's worth of water. So I started putting my mug, funnel, filter, and coffee on a digital scale with tare, and remembering how much each size holds in dry ounces. It avoids the situation in which I'm waiting for the water to run out to make sure it won't overflow; I just pour until I hit the right weight and then go do something else until it's done.
The compass is still terrible though!