IF you employ Atlas flex track and run into the problem of locating the center holes due to track being already installed in layout, having forgotten to first punch through the holes from the bottom, do this: If section of flex is original 3 foot in length, take another new 3 footer, flip it upside down and line up the ties end to end next to installed one..You will of course now see which ties you can put a push-pin through, into their centers from above...Or, just count them ..
