which is more accurate direct weighting or weighing by difference?

I think that's a debatable question. Also I think the answer depends somewhat upon what you are doing. For quant work, where you want the weight of a sample or the weight of a ppt I believe weighing by difference is preferred. In SOME cases it may be more accurate and precise.

Direct weighting and weighing by difference are two common methods used in weighing applications. The accuracy of each method depends on various factors. Let's take a closer look at both methods and their accuracies:

1. Direct Weighting: This method involves placing the object to be weighed directly on the weighing scale and recording its weight. It is a straightforward and simple method. The accuracy of direct weighting depends on the accuracy of the weighing scale used. For higher-precision balances, such as analytical balances or precision laboratory scales, the accuracy can be very high, often up to several decimal places (e.g., 0.0001 grams). These balances utilize highly sensitive load cells or electromechanical sensors to provide precise measurements. Therefore, if a reliable and accurate weighing scale is used, direct weighting can provide accurate results.

2. Weighing by Difference: This method involves measuring the weight difference before and after adding the object to be weighed to a container or vessel on the weighing scale. Initially, the empty container is weighed, then the object is added, and the weight of the loaded container is recorded. Finally, the weight of the empty container is subtracted from the weight of the loaded container to determine the weight of the object. The accuracy of weighing by difference is dependent on several factors, including the accuracy of the weighing scale, the precision of subtraction, and the choice of container. It's important to use an accurate weighing scale and ensure that the subtraction process is carried out meticulously to minimize any errors.

Overall, both direct weighting and weighing by difference can provide accurate measurements if performed correctly with appropriate equipment. Direct weighting may offer higher accuracy if a reliable high-precision scale is used, whereas weighing by difference can be suitable for situations where the weight of the object itself is small compared to the container or vessel used. It is always recommended to consider the specific requirements of the weighing task and choose the most appropriate method accordingly.