please introduce an option to input weights of diary items by difference (eg. jar before and after)
It would be very helpful, and save a of of hassle and time jotting down weights on a piece of paper and then using a calculator to subtract and finally inputting the result into Cronometer, if there was an (optionally enabled) feature, that for each diary entry, the user would enter two weight amounts, not just one. And the amount Cronometer would actually consider eaten, would be subtraction of the second weight from the first.
Two major cases where this would be useful:
Getting any ingredient out of a jar, especially when not adding it all at once, but adding some amounts from the jar a few times over time, for example when frying on a pan and adding fat. I often have a jar of ghee sitting by the stove, and add more as I need, and then with my steaks I consume all ghee on the pan. The only way I can manage accounting for the amount ghee I have eaten, is weigh the ghee jar before and after cooking, and use the difference between the two weights.
Weighing a food item before eating it, but then not consuming all of it, either because its too much, or it has inedible refuse. For example fish, I weigh the fish before I eat it, but then bones remain and I need to subtract that. It's a pity Cronometer doesn't have the functionality for this, it would make life a lot easier, and without oily sheets of paper in the kitchen (oil on paper makes it difficult to write with a pen). You could also use that when weighing a vegetable as bought, and then weighing the cut-out inedible parts at the end of cooking, and putting that value in the second column.
So there would be two weight columns, and on items you don't need this feature for, you would fill only the first one, and the second (could be labeled "Refuse weight") would be considered zero. If the second weight column would be filled, the value from it would be subtracted from the first value, and Cronometer would use that difference for all calculations.
Of course the feature could be completely turned-off by default in Settings, so that not to confuse users who don't need this, but whoever would find it useful, could turn it on and only then see the two weight columns, instead of just one.