Weight sensor, how to measure something light?

Question

Sensors

A sensor is needed that can measure the weight of ordinary sheets of paper. But in terms of area, at least 10 by 50 cm (I imagined that this was some kind of flexible and sensitive plate that reacts to the slightest weight).
Those. you need to somehow accurately measure the weight and so that he can signal that the weight has changed.

Answer 1

It is not entirely clear what you need - to measure weight constantly or signal a deviation from a specific value.
If you just measure weight - electronic kitchen scales (for example, Sonax SF-400A, with an accuracy of 0.1 g).
More options:
- google "load cell";
- use the system of levers + electronics to it;
- use laboratory mechanical scales .

Answer 2

if you have time and desire, then look towards arduino or similar