This would not be classed by many as a "slide rule" in that it performs no calculations. On the front you have a list of uses for concrete with an index number associated with each. Moving the slide so that the index number appears in the window tells which company produt you should use and its proportion.

When you reverse the rule, in a similar window, you can see how much cement, sand and aggreggate you need to use. The data being presented in different ways and units.