longest/shortest day shadow clock

I had wondered what the easiest way would be to determine the beginning of the year...the equinox or more accurately the equilux when I happened across this video. http://www.youtube.com/watch?v=okRBa6yW1Mo

It is just a basic sundial but only measures the length of the shadow of the sun. The longest shadow is of course the winter solstice, the shortest the summer solstice. Using a simple pile of rocks or marks on a stick one could count the days between them, use half the marks or half the stones to count to the equinox.

Pretty simple.