I should have probably done a better job explaining the operations, constants, variables, simple expressions, etc... The input expression is basically a function of the current position on the X axis <x>, and the current time <t>, so you'd get an ascending line with the expression "x", and a descending line with the expression "-x" for example. Any non existing constant or variable such as <a> and <b> would resolve to zero but I should have also made it clear that they were placeholders in that F1 panel. Anyway, thanks for the feedback.