For whatever it's worth, I've been dismissed or disbelieved by medical providers while measuring with pads, measuring with tampons, and measuring with cups. With cups, the biggest trouble I've had was that a number of providers were only familiar with alarming amounts in terms of pads/tampons per hour; they didn't really know what to do with a millitres per hour stat. Equally problematically, I've had providers say to me, "Sometimes, we can think we're soaking a tampon when we're really not. The outside might be red, but we haven't really bled all that much."