Some years ago we did the comparison between weighing a cat on multiple bathroom scales and by "hanging" the boat under our (accurate) 250kg scales (dedicated scales for just this type of weighing) and we found that 1. Bathroom scales are notoriously inaccurate, and 2. There was quite a large discrepancy between the weight from the bathroom scales and the correct weight, (as much as +/-15kgs in 200kgs total)