The circle areas of the Porton reticles increase with Root 2 progression as do the divisions on the right hand side of the rectangle. These divisions are numbered for convenience. Rectangle size is 4.5mm x 2.025mm. The specimen is racked on the mechanical stage of the microscope and traverses are taken right across the deposit sizing all the particles encountered.

Reference: K.R.May, Journal of Scientific Instruments Vol. 22 Oct 1945. “The Cascade Impactor.” An instrument for sampling coarse aerosols.

Glass Type and Thickness

Soda Lime 1.5mm thick

Diameter Tolerance

+0/-0.1mm

Orientation

Correct reading through glass