Here is a real life problem from a silica bricks factory in a small industrial town in India. There are illiterate workers who cannot identify decimal digits. The management team of the factory is trying to figure if there is a way for these workers to operate a digital weighing scale to fill buckets with a certain mass of a given material. For example, they may be asked to fill 5.3 kg of a certain material in the bucket, i.e. decimal fractions are involved.

If the factory were using a beam balance, this would have been an easy problem to solve. The workers could then place the required weight in one pan and keep pouring the material in the other pan until the beam appears to be balanced.

However this factory uses a digital weighing scale which involves recognising decimal digits to read the measurement. What do you think is the easiest way to train the workers to do their job without having to teach them how to count?

I have a solution in mind which would involve configuring the digital weighing scale in a certain way for every measurement the workers have to make. I will propose this solution to the management team of the factory. But I would like to know any suggestions you have and take them into account as well before proposing my solution. I will also share the solution I have in mind after learning about your suggestions.

Update on 08 July 2010: Prunthaban has suggested a solution in the comments section which is pretty much what I had in mind too. I will propose this solution to the factory. The solution works like this: Say the worker has to fill 5.3 kg of a certain material into the bucket. A literate supervisor first places 5.3 kg of that material on the weighing scale. The instrument now shows "5.3 kg" on its display. Now the remainder of the solution assumes that the digital weighing balance has a calibration wheel to calibrate the instrument. The supervisor turns the calibration wheel until the display shows "0.0" kg while the 5.3 kg of material is still placed on it. Now the material is removed from the balance and the display shows "-5.3 kg". Now all a worker needs to do is pour the given material on this calibrated balance until the display shows "0.0 kg". As long as the workers can be taught to recognise the digit "0", this solution should work fine.

Update on 05 Aug 2010: The above solution was successfully implemented in OCL India Limited, the silica bricks factory where this problem was faced. The digital weighing balance involved in the problem indeed had a calibration wheel, so the above solution worked for them. Thank you, Prunthaban and others who participated in this discussion.