Mass is measured using balances, and the two methods for weighing mass are called direct weighing and weighing by difference. Direct weighing is when an object is placed on a balance and the mass is read. Weighing by difference is done when two measurements are taken and the difference is found between the two weights.
A few things to consider when weighing directly.
- Always make sure before using a balance that it is level.
- Place a piece of weighing paper on the balance to protect it, do not weigh directly on the pan.
- Do not add chemicals to a container or on the weighing paper when on the balance.
- Never weight cold or hot items.
- Clean up any mess on or around the balance immediately.
To weigh by difference, first measure the mass of an empty container, then measure the container with the substance that the mass is being calculated. Subtract the empty container´s mass from the mass of the substance.
Most new scales have a taring option. The scale will automatically subtract the weight on the scale from all future calculations when the tare button is pressed. If an empty container is put on the scale and the tare button is pushed the weight of that container will not be calculated or displayed thereafter. This allows a substance to be weighed in a container without having to consider the container weight.