You can make a stepped attenuator using any values you like. It's a pretty easy thing in principle, just a lot of resistor pairs to form voltage dividers with precise ratios where both resistors of the pair add up to the same value. It makes a precise divider but switch contacts sometimes click as they go open for an instant before closing on the next resistor pair, or vice-versa.By the way, I've put an OrCad schematic file online. If everyone would rather standardize on a different platform, I'd be happy to upload alternate file types. The nice thing about OrCad is that it has the option of laying out circuit boards and running PSpice analysis. We'll probably not have boards etched, but we may use Spice for some what-if analysis at some point in the future. And having a format for distributon of schematic drawings that allows easy modification of the schematics is nice too.