Welcome back!
So, your mental image of the role of sugar and the eventual sweetness seems to me to be a bit off. Let me explain.
When you add sugar, you are increasing the eventual alcohol content. In general (for a home winemaker), all of the sugar that you add before fermentation will be converted to alcohol, and your cider or wine will be dry (meaning, no sugar left). It will not be sweet. You add as much sugar as you want in order to achieve a desired amount of alcohol (known as ABV).
To get a sweet final beverage, you must "backsweeten." This means that, after fermentation is finished, you "stabilize" the cider/wine by adding potassium metabisulfite (i.e., Campden tablet) and potasium sorbate. (Potassium sorbate prevents the yeast that are in your cider from multiplying.) Then you can add sugar to make it as sweet as you prefer, and that sugar will not be fermented into alcohol.
BTW, the tool to measure the specific gravity is called a "hydrometer," not barometer.