The calculation is realistic, but requires ideal conditions. For example, a suitable fermentation temperature for the yeast and manageable alcohol strength and a good nutrient supply.
If you click on one of the fruit varieties in the list, its sugar content and non-fermentable substances are automatically entered into the calculator. In the case of stone fruit, the calculator will ask you whether you want to ferment with or without stones.
There are two ways to use the calculator:

1. After adding water and before adding sugar, measure the specific gravity (SG) of the unfiltered, but as finely mashed as possible mash, and enter this value in the field provided. Why after the addition of water and before the addition of sugar? First, because the mash is at its most liquid at that point, which makes it easier to measure, and second, because you may want to add the sugar later. For the %wt of unfermentables and %vol of stones, use the table as a guide.
2. Do not measure and instead use the values in the table directly and adjust the values entered for the %wt sugar, the %wt unfermentables and %vol stones at most slightly, depending on what impression you have of the fruit.

Two somewhat uncertain variables are the density of the stones and the density of the other unfermentable substances. At the moment we assume 1.04 kg/lt for the stones and 1.45kg/lt for the other non-fermentable substances. But these can be changed here:

Density of stones: kg/lt
Density of the other unfermentables substances: kg/lt

On the one hand, the stones are made of quite heavy material, on the other hand, they are porous and have air chambers. Therefore, they can partially even float on the mash before fermentation, so they have a lower density than the mash. Then, when the air is displaced by liquid during mashing and fermentation, the density of the stones increases. Since most of the data calculated here is for before fermentation, the low density of the stones before fermentation is more applicable to the calculation.
The unfermentable matter is all that remains when the water and fermentable sugars are subtracted from the pitted fruit: Fiber, organic acids, unfermentable sugars and starches, protein, fat, sugar alcohols such as sorbitol, and minerals such as potassium.
The calculated "liters without stones" gives a more accurate information about how much mash will be in the still after removing the stones.
The calculated "measured value of pitted fruit", i.e. the measured value before adding water and sugar, may be interesting if you measured the fruit with a refractometer before mashing. The data refer to measurements with a density meter, but in this case, where there is no alcohol yet, we suspect that the measurement result is not fundamentally different.
The calculated "liters sugar water" (i.e. the liter mash minus the liter unfermentables) as well as "%abv alcohol maximum in sugar water" are probably useful for further calculation with our Distillation Simulators.
The calculated measured values can be output as SG, Oechsle, density, Brix and Plato. The calculated measured value after fermentation refers exclusively to a density meter. A refractometer shows a much higher value after fermentation.

The measurement data %vol stones and density of stones are from forum members: