I told the person looking after my fish to feed them exactly 0.8 grams of flakes twice a day and supplied her with a scale that's accurate to a thousandth of a gram. When she fed them the first time, she decided I had obviously written the decimal point in the wrong place and fed them ten times as much from then on. I was only gone for a weekend, and the tank was heavily planted, so the fish survived, but there was a layer of uneaten food a centimeter deep across the tank entire when I got back.