Weighting On Technology

With all of our modern technology, I'm surprised I haven't come across a scale that you can program to suit your needs. For instance, I don't, at the moment, want to know how much I weigh. But I WOULD like to get on a scale daily or weekly and see how many pounds I've LOST without knowing my weight. But I'd like the scale to keep track of my weight so that when I'm ready I can refer to my weight history. Did I just give away a great idea or is this product already out there and available to the public at an affordable price?