Spring scales are weighting balances that need to be hung to make their measurements. They are made of a spring with a loop at the top end for fixing and a hook at the other end to hang what need to be weighted.
The first record of a spring balance is found in Great Britain around 1770 near Wolverhampton. The inventor incorporated the company of George Salter & Co., who patented the spring balance in 1838.
A spring scale is are also called Spring Balance is very simple: it only uses gravity and Hookes law to operate.
However, it only measure mass (the force of gravity) and not weight and the reading may depend of where you are on the Earth surface. For that reason they are marked with a mention similar to: “no legal for trade”.
Because of their simplistic conception, competitive cost, robustness, ease of use and rapidity, it is a very popular way to take quick measurements that don’t need to be 100% accurate, like babies weighting in developing countries up to silo storage loads in farms.