At the end of my last column, I had discussed how to do a graduated sieve analysis of a sand and gravel aquifer and hinted at how we might select our screen openings from this. As you will recall, I described how we could plot the analysis of our formation on graph paper with slot openings or grain size in thousandths of an inch on the horizontal scale with zero at the far left. The vertical scale will list cumulative percent retained from zero at the bottom to 100 at the top. If we plot what our graduated sieves have retained, we will develop an S curve or we can simply connect the dots as a child might do.