A spring balance (or newton meter) is a type of weighing scale. They are commonly used to measure the force exerted on an object. This force is usually measured in Newtons and is essentially the weight of an object. The weight of an object is a measurement of its mass x gravity (W=mg).
Spring balances consist of a cylindrical tube with a spring inside. One end (the top) is usually fixed to an adjuster which can be used to calibrate the device. The other end is attached to a hook on which you can hang objects. As objects are added, the spring stretches and the resultant force can be read from the scale.
There are many types of spring balances available. The more robust models are often found to be the cylindrical forms however, many models are prone to overextension of the spring mechanism if excessive weight is added. Choosing a model which does not allow the spring to be overstretched will increase its lifespan as well as to provide a more accurate reading over time. Ensure spring balances are calibrated to read 0N when no mass is attached before use.