In method 1 we assume that, from the moment of birth, cells move
deterministically through state space 
. This allows us to
represent the current state of a cell with a function of time.
Synchronization experiments are generally successful in obtaining cells
which all have yet to enter the cell stage the experiment is focused on, the
oldest cell being the first one to enter the cell cycle stage of interest.
We therefore construct the distribution p(t,a) at time t around the
oldest cell
i.e. all cells are younger than the time the sample is taken. Since the start of the experiment is an arbitrary point in time we are allowed to use negative ages. We now can rewrite eq. (1) as
where a is a variable comparable to the age of a cell. A further consequence of this distribution is that we actually are following a single cohort of cells discarding their offspring.
As soon as we know the precise form of distribution p(t,a), f(a) can be uniquely determined by
where 
is the i'th derivative of the average output with respect to
time and 
is computed as
in which 
, which reflects the
i'th moment of distribution p(t,a).
