Was in the garage yesterday. Took a picture. You can buy a cheap accurate digital platform weighbridge for just over a hundred pounds. This can weigh 600KG.
The flat square thing is the part you park on. The folding ramp that I just dropped, is on the floor in the way... The white plastic part with all the figures on it is wireless, and hooks on a nail in the wall.
You can weigh a chair, alone. Or you can weigh that chair while you are in it. So you can drive on, and off every day to see your weight. Just deduct the chair.