2) The inventory technique
In the inventory technique, there are two ways to obtain the mass of an item. One way is to measure the
dimensions of the object and then the mass is determined by multiplying the measured volume with the corresponding density. The other way is to weigh the commonly encountered items in advance or get their weight
from the manufacturers and then create an inventory list. Thus, the mass of surveyed items will be estimated based
on the inventory list. This technique can be used for items that cannot be weighed. The problem is that sometimes it
is difficult to determine the volume of irregular shaped items and the density of various types of materials. Error will
arise when the surveyed item is mismatched with the ones from the inventory list.