Place the draft shield and cover on the balance. Push the
"tare" button. The mass reading should be 0.000 g. Remove
the draft shield cover, and place the weighing vessel on the balance
pan. Replace the cover, wait for the mass reading to stabilize,
and record the mass using all digits displayed. Remove the weighing
vessel from the balance and add the desired amount of material.
Replace the weighing vessel and the cover and record this mass.
The mass of the substance of interest is equal to the second mass
recorded minus the first mass recorded.