The AF200 uses a revolutionary waisted measurement chamber (see left), with a central section of 5mm diameter, widening to 7mm diameter near the condenser (top) and the measurement orifice (bottom). The RH and temperature sensors are built into the narrow section, with six small holes connecting the sensor chamber to the measurement chamber.

Compared with a cylindrical measurement chamber, the main advantage of this design is a reduced sensitivity to probe angle.

A further effect of the waisted chamber is to reduce the perturbation of the sample surface microclimate, with increased RH at the sample surface for a given flux.