Harder floor is always better than softer floor. On some scales you can change your weight by several pounds depending on where you place your feet. It is best to do it the same every time. The feet should be placed so they are centered on the scale. If it still does not give accurate results, it may be either defective or a very cheap brand (regardless what you paid for it). We got one once ($29.00) that i could gain or lose 5 pounds based on if I gently stepped on it our stepped up like I normally would! It went back to the store and we got one for $49.00 that worked great, matched the dr office scale and lasted a long time.