I recently bought two electronic scales, originally to weigh parts and counterweights I put in 'Streets vehciles, etc., and to help mix paint accurately each time. But and have found them to be amazingly useful in modeling and just - to have.
Both are well made and incredibly easy to use. Together, theycost less than a single good scale O-gauge reefer. (I pondered this last night over a glass of wine before I decided it is both very revealing about what features cost money in this world, and that it is just they way things are, whether I like it or not.)
The big orange one in the photo is an Escali 157 (they come in various colors). The small one sitting on it is an AWS Gemini-20. Either will determine the weigh of something in grams or ounces, as you wish.
The Esali 157 will weigh anything up to 7 KG in .1 gram increments. It cost $35.
The Gemini-20 will weight only up to 20 grams, but determine weight to 1/1000 gram. It comes with calibration weights and a procedure whereby you can calibrate it to 1 milligram accuracy. it costs about $25.
The pencil I have provided to show there size weights 4.472 grams, by the way.
The smaller one is an AWS Gemini -20. It weighs up to 20 grams to the thousandth of a gram.