Cosmic rays may cause soft fails in electronic logic or memory. The IBM Journal of Research and Development, Volume 40, No. 1, discussed this complex event in detail. In order to predict electronic fail rates from cosmic particles, it is necessary to know the local cosmic ray flux. This paper reviews the penetration of cosmic rays through the earth's atmosphere, and the parameters which affect the terrestrial flux. The final particle flux is shown to vary mainly with the site's geomagnetic coordinates and its altitude. The paper describes in detail the quantitative cosmic flux at one datum (New York City) and then tabulates in an appendix the relative level at other major cities of the world.