http://www.engineer.cc/tools/sliderules.html
(X) This one is complete with a numeric readout of the cursor position! It's really useful if you're unfamiliar with reading the various scales.
If you're not sure about how to use a slide rule, take a look at Slide Rule Calculations by Example. It's a self-guided demo that demonstrates different calculations by simple examples. Also included is How to Use Your Pickett Slide Rule, a simple 4 page manual.
These pages should work in modern browsers that support the JavaScript and W3C DOM standards. These slide rules have been tested in Internet Explorer, Firefox, Safari, and Google Chrome. It should be noted that the virtual slide rules were made possible by Walter Zorn's Drag and Drop for Images and Layers.