The wet feet vs. dry feet thing will make a big difference in readings, that's why I'm not a fan of the built-ins on scales and prefer to use my handheld meter. (My hands are more consistent as far as humidity levels go.)
It's similar to the issues with HRC pads on sports equipment. I work support for an equipment manufacturer, and holy cow you can't imagine how many people call up with issues regarding HR problems during the winter! Forced air heating, no humidity, dry hands, etc. and they wonder why the machine can't read a transdermal nanocharge. (Gyms/clubs with the AC on full blast in the summer have similar issues.)
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"I feel like my world was classier before I found cyclocross."
- Mandi M.