use this tool to be able to find the direction and flow of dual color filaments dial in the middle will give you the indication of where your transitions start and stop while the heart at the bottom will allow you to have a greater view of the transitions as well as be able to use as a pointer, works with all qualities fun and simple tool.

its hard to tell with the filament i used in the picture but in person you will see the color segments on the dial in the direction of the color change as well as where the transition starts and stops.

ps if you flex the heart you will get a pop off color wheel and a pretty cool heart with infill patern ;-)