The Fisher Sub-Sieve Sizer, one of the most widely used instruments, is characterized by its poor readability in the high porosity, low micron region. In this region readings are not only prone to subjective operator errors, but they become impossible to determine in low micron ranges (below 2 microns approximately). The method proposed in this article eliminates this difficulty, and extends the readability to as low as 0.4 microns without any alteration of the instrument itself. This makes it possible for any user of the Sub-Sieve sizer to greatly extend the capability of his instrument.