All of this also brings up a good point in that some may think it is a MAJOR hassle to check calibration/slope. As TR pointed out, it really isen't hard to do. All you need is an ACCURATE weight(20kg is what I will be using with quarq) and like 5 minutes. You can also measure your weight at USPS to see if you can get +-2%.
edit: sorry to hear gsteinb