What is the difference between arbitrary and natural levels? why do these matter? (4) how do archaeologists recover the smallest artifacts and ecofacts?

Arbitrary level refers to the fundamental vertical subdivision of an excavation square, implied only when easily identifiable natural strata are absent and when natural strata are more than ten centimeters thick.  

Natural strata refer to a vertical subdivision of an excavation square, which is reliant on the natural breaks in the sediments in terms of grain size, color, hardness, texture, or other features.  

It is important to know the difference between the arbitrary and natural levels as arbitrary levels could amalgamate artifacts from distinct natural levels, that is, of distinct geologic contexts.  

The archaeologists can recover the smallest ecofacts and artifacts with the assistance of flotation, screening, and bulk matrix processing

this is math not biology xd