The difference in mechanical balances is in function of its principle of operation. Scales measure the force exerted by an object subject to the force of gravity, while the scales measure the weight of an object by comparing it with a known scale.
Just as the scale is used to weigh large and bulky masses, the balance is used to weigh smaller masses of only a few kilos, being usual for example in laboratories.
When we talk about scales or electronic scales, the difference is not clearly defined. In general terms, scales are used to weigh large masses, although the precision (d) is smaller. On the other hand, the opposite is true. It is quite common that the scales have a platform at ground level, where it is easy to place the mass to be weighed. In general terms, it is usually accepted that up to 30Kg capacity, the instrument is a balance. For larger capacities, a scale is considered.