Sounds like there might be more room for error with this method (what's stopping you from pushing your hand in at the last moment without realizing it and marking the wrong blade?). A visual check would still be in order to ensure proper tracking I think. Another method I saw awhile back instead of using tape, use some dry erase marker on the tips of the blades, it adds no weight and it gives you the color reference you need. Best of it all it washes off . Would only work properly on white blades of course, but still.