Abstract: A method for processing data produced by a chemical sensor to predict a rate of diffusion and steady-state level of a chemical vapor absorbed by a coating applied to the chemical sensor. A chemical sensor (10) includes a surface acoustic wave device (12) in which a polymer coating (34) is provided to absorb a chemical vapor. As the vapor is absorbed by the polymer coating, a resonant frequency associated with the SAW device changes in proportion to the mass of the vapor absorbed. The change in resonant frequency is periodically sampled by a high-speed counter (58), digitized, and filtered by a microprocessor (100). In processing the filtered data, the microprocessor describes each data point as a constraint line in a (.tau.,C) space, where .tau. corresponds to the rate of diffusion of the chemical vapor into the polymer and C corresponds to the concentration of the chemical vapor in the polymer at a time t. A minimum energy function L(.tau.