It is difficult for an illiterate worker to use a beam balance too because the worker may not know what denominations of weights to put in one pan.

It is easier for an illiterate worker to use a digital scale because it shows the numbers. You can print all the weights on a paper, give it to them and ask them to put the material until the number in the paper matches the number in the meter.

Vivek,

In a beam balance, once a supervisor tells them which weights to use, their job is easy. They only need to keep pouring material until the beam becomes balanced. If the beam tilts towards the pan with the material, then they need to remove material.

With a digital scale, however, the usage becomes more complicated than it sounds in your comment. Let us say the workers are supposed to pour 5.3 kg of material. They pour a little too much material and the scale shoots up to 6.2 kg. Since the workers cannot read the digits, they don't know whether they should keep pouring more material or remove material.

The digital balance has to be designed in such a way that a given weight can be preset. When the worker fills the bucket and the total weight reaches the preset value, the digital balance can alert the worker either by showing a green light or by beeping. The worker must be able to notice this alert and stop filling more.

Veera,

Your solution would work fine if the factory had some control on the design of the digital weighing scale. However in this case, the factory has no control on the design of the digital weighing scale. They have to work with what they have. Therefore your solution will not work in practice.

Here is my solution: Most digital scales have a button called "Set to 0". Let us say I want the people to weigh 5.3 kg. I keep 5.3 kg weight on the scale and press "Set to 0". After I remove this weight, it shows "-5.3". Now the worker only needs to pour until the scale shows "0.0". The worker just needs to know "0" to do this. To know whether to pour more or remove from the balance, the worker just needs to look at the "-" sign. If it is there keep pouring, else remove. :-) So the worker can achieve the task by remembering "0.0" and "-" signs.

Prunthaban,

Your solution is pretty much what I had in mind too. I proposed this solution to the factory management and it was successfully implemented in the factory. I have updated my blog post with these details. Thank you for participating in this discussion and offering your solution.