Line Perpendicular to a Plane

This is a picture of a sun clock. A sun clock is a stone used to tell time in relation to the sun. This object is always found outside, since it requires the sun to use. In the real world, there are not many people who use it. I traced the plane in red and the perpendicular line in purple. The purple line is perpendicular to the rest of the clock because the perpendicular line intersects with the plane.  http://www.google.com/imgres?um=1&hl=en&client=safari&rls=en&biw=1186&bih=640&tbm=isch&tbnid=dwAOIC8E-1yseM:&imgrefurl=http://et.wikipedia.org/wiki/Pilt:Sun_clock_in_Valka.jpg&docid=DBJe9qIHV-amBM&imgurl=http://upload.wikimedia.org/wikipedia/commons/f/fc/Sun_clock_in_Valka.jpg&w=640&h=480&ei=gcWJUPzMA82I0QGNz4C4Aw&zoom=1&iact=hc&vpx=115&vpy=186&dur=5593&hovh=194&hovw=259&tx=185&ty=123&sig=101161591993119626923&page=1&tbnh=135&tbnw=168&start=0&ndsp=18&ved=1t:429,r:0,s:0,i:96