Mark the place on the bathroom floor (not mat). Mark foot-shapes on the scale tread. Take the bottom off the (spring-type) scale and vacuum out and zap with CRC/WD40.
Then it should be consistent, if not accurate. As has all been said above.

Reminds me of the time we fished a match organised by a small fishing club. At the weigh-in, the official, with a VERY rusty spring balance called my pal John's catch at 3lbs. "Never in this world!" says John. The official looked at him (big man) and jerked the hand holding the balance up and down. "5lbs 2oz" he calls.
Later he approaches John and asks if John thinks that soaking the scale in oil would improve things. 'Well, says John, that's ONE of the things you could do with it."
Still don't know how I kept a straight face.