Here is an app that delivers exactly what is promised. The Cell Frequencies app is a simple but useful reference for immunologists who wish to know the, well, frequency of a particular cell type in human blood. In total, 27 cell types are represented in the app, including everything from lymphocytes, to regulatory T cells, to eosinophils. Once a cell type is selected, the frequency (expressed as cells per milliliter of blood) is given, along with a percentage (either of a larger cell class or of total blood volume). For instance—in case you’re curious—there are 0.03–0.3 x 106 eosinophils per milliliter of blood, and this cell subclass constitutes 0–7% of the leukocyte population. In other sections of this app, users can view all cell types in a chart format (and can request a copy of the wall chart), as well as peruse a few protocol videos employing Stemcell Technologies products.