The most accurate scale on the market reportedly is the Brecknell ElectroSamson handheld scale with a jaw clamper added. It’s what you see on Major League Fishing and what the major circuits use for catch/weigh/release tourney formats.
It’s spot on. I compared it to my electronic kitchen scale.
$80. One year warranty. Fyi, very minimal water resistance. It wasn’t designed for the boat. I honestly think I fried my first one due to boat locker humidity after leaving it in a ‘dry’ rod locker for a couple months in the summer.