In many forensic situations, the amount of soil, sediment, or dust material recovered for analysis is too small to allow bulk methods of analysis to be used. There are also many situations where the objects of interest are single pieces of rock, brick, or concrete, or a relatively small number of gravel-sized particles. The weight of an individual particle can be accurately measured using an electronic balance. In the field, it is practical to weigh rock fragments and gravel particles up to 5 kg with an accuracy of 0.1 g or better, using a batterypowered digital balance, whereas in the laboratory, individual sand grains can be weighed with an accuracy of up to 0.001 g using an analytical balance. A sphere will have a ratio of 1 and all other solid bodies will have a smaller value. However, as noted earlier, surface area is impractical to measure, and volume is difficult to determine accurately for small particles.