Gravimetric determination of ice sublimation rate

It is common practice to measure the drying rate of individual vials by a gravimetric method in which the primary drying cycle of a batch of pre-weighed vials is interrupted after approximately 25% of ice has sublimed. The vials are re-weighed and an average drying rate determined from the loss of mass, divided by the time period from the point at which sublimation starts to the point of interruption. A number of issues are explored in this Figshare document which question the validity of the drying rate so determined, and in particular the fact that the method at best provides and average drying rate but over what period of time, it is difficult to judge.