Answer:
Electric currents
Physical properties of metals
Influence of gravitational force on objects
Explanation:
The engineer who designed the digital scale must have a good working knowledge of the electric current, and its principle of flow through various materials, and also, factors that can affect its flow through a material (especially metals).
The physical properties of metal would have to be known by the engineer, in order to design the digital scale. The engineer must be able to predict some of the effect of the changes in the physical properties of a metal, and then use this to get some function that he wants from the digital scale, especially the effect of these physical changes on the electrical conducting ability of a metal.
The knowledge of the effect of gravitational force on objects is a must-know for the engineer. The process of scaling here on earth is very much dependent on the gravitational pull on objects downwards to the earth. This knowledge can be used to predict how much deflection this gravity forces will induce on an object towards the earth.
