Because there are no units, the equation can only be used to compare one rate of work to another rate of work at a different time (or a different deadline).
ratio of rate of work at time t1 compared to rate of work at time t2
= rate_of_work(t1, d) / rate_of_work(t2, d)
= (1 / (d - t1)) / (1 / (d - t2))
= (d - t2) / (d - t1)
This works because the only variables left are in the same units, even if that unit itself is unspecified.
What unit is the 1?
Because there are no units, the equation can only be used to compare one rate of work to another rate of work at a different time (or a different deadline).
ratio of rate of work at time t1 compared to rate of work at time t2
= rate_of_work(t1, d) / rate_of_work(t2, d)
= (1 / (d - t1)) / (1 / (d - t2))
= (d - t2) / (d - t1)
This works because the only variables left are in the same units, even if that unit itself is unspecified.
could a unit for this be s-1?
Its a factor. It doesnt have a unit.