This sample contains a 3dsmax floating point controller plugin that takes two values and multiplies them to create its output. Just download and compile.

Download "Control" Plugin Sample

You need to make sure that Autodesk.Max.dll assembly is properly referenced for your version of 3dsmax, by default the project references the assembly in "C:\Program Files\Autodesk\3dsmax2010\Autodesk.Max.dll" but you can change this to any path.

After compiling simply copy the generated .dll file into 3dsmax plugins directory.