When a truck arrives at the scale, you can capture the truck's empty weight (its tare) by going to the Trucks screen. Find the Trucks screen by clicking the dump truck icon in the menu at left.
The Trucks Screen
Or you may simply type the existing Truck ID and press Enter on your keyboard.
All recorded tares, edited trucks, or other changes made at the desktop application will be sent up to the Fast-Weigh 10 Web Portal upon syncing.