Besides the obvious technological differences between digital and medical style (counter balance) scales why do they weigh me differently?

tenchu11
So i've been using medical style scales at the gym and at work on an oil rig camp where they have gyms to keep us that want to stay in shape well work out. I went to two different camps and the counter balance scales (medical ones) both had basicly the same weight for me in the morning give or take 1 to 0.5 lbs. When I got home I noticed the digital scale added an extra 4lbs even after I didn't eat that morning and used the bathroom. I read up and saw that digital scales tend to be less accurate than counter balance ones and tend to give a higher weight, why would this be?
Besides the obvious technological differences between digital and medical style (counter balance) scales why do they weigh me differently?
5 Opinion