The term from the General Equation is:

$$\left(\frac {\partial C}{\partial t}\right)_{production} = \space a(x)R(x)\\$$

This described the rate at which the concentration of dead tests

Tests are added at some nominal production rate. For convenience, we split up the production into two components^a: (1) the population size or standing crop ($a$); and (2) the population turnover or reproduction rate ($R$). The standing crop is a concentration of living individuals - i.e. per cm³ of sediment - while the turnover rate is per time quantity (e.g. yr^-1). So we can define the production rate mathematically as,

$$\frac {dC}{dt} = aR$$

and therefore the production rate ($\frac {dC}{dt}$) is in individuals per cm³ per year (i.e. cm^-3 yr^-3).

In essence, the reproduction rate $R$ is a simple proportionality term linking standing crops with dead test production rate. For example, if the standing crop is 100 individuals per cm³ and this population turns over twice a year, then 200 tests ($a \times R = 2 \times 100 = 200$) will be produced in that volume of sediment within 1 year. Put another way, if the standing crop is 100 individuals per cm³ and there are 200 dead tests per cm³ added in 1 year, then the turnover rate is 2^b.

When we introduce sedimentaton, and can therefore conceivably explain the accumulation of all dead tests within a given sediment deposit, we will see that $R$ is one of a few possible parameters that link the two things that we can directly observe, standing crop and dead test concentrations.