The post from Lako is, I believe a reference to the Name of the poster before him "Ramzoom" who references owning a scale shop at some point.
We used a lot of scales when I was in culinary school. A 'tare' weight or button is used to negate the weight accumulated on the pan.
For example, on a 3 beam balance baking scale, the tare weight weighed as much as the pan used to hold the ingredients.
Some really old or cheap digital scales can only use a tare once while adding weight (presumably to negate an empty container), a lot of the new ones you can use the tare button repeatedly to stack amounts together.
get something that you know the exact weight of in order to keep an eye on your scales calibration as well.