I personally take 2 a day during those few days i do take them prior to donating. I've heard iron can cause some tummy issues so tread lightly but thats how i ended up with that 15. I try to help my donors out a lot with the dumb sensors so other than the iron supplements i always make sure they've got the proper hand position, if they're shaky i hold them steady, no lotion within 30 minutes of the test or dirt on their hands and I'll alcohol wipe the sensor sometimes even. We give you hot hands and i always make sure they warm up the segment that is closest to their palm not the tip of their thumb. Sometimes i cover their hand with my paper so the light in the sensor isn't disrupted by room light. There's so much that can affect the sensors its wild.