3dsmax has built-in expression controllers which allow quick math operations on one or multiple controllers. To use an expression controller you need to add 'X Expression' where X is the type of the output you desite. For example, for floating controllers you'd have Float Expressions.
Once an expression controller is added you can either wire existing controllers into it or new ones by dragging out the 'Add Variable' slot. Automatic variable name will be assigned. To change the expression simply rename the controller (for example, 'X*Y' will multiply variables X and Y together).
NOTE: Expression controllers will reference all wired-in variable controllers with the scene by adding them to the global 3dsmax float or point3 tracks. This is required because the controller needs to be able to get the sub-controllers through the scene's sub-anim tree.
Script controllers behave very much the same way as expression controllers. They have an Add Object and an Add Node slots which can be used to assign new variables. You can assign any object type, including other controllers to the Add Object slot. You may only assign scene nodes to the 'Add Node' slot.
NOTE: When adding controllers to the 'Add Object' slot you cannot use their value directly. You need to add 'X.Value' to operate on their values. So, for example, if in expression controller you had "X*Y" in script controller you'd have "X.Value*Y.Value"
