What's this all about?

Over the past few weeks we have been going through the design and development steps in building a 32 foot Town Lattice Truss covered bridge for the Village of South Wayne, WI. For my "proof of concept" in the process I am building a 3/8 scale model of this bridge truss design. 

There is much to see and learn. Can you figure out what is going on in this picture?  How and why?

Why the dial calipers?

During an interview with Art Hackett, from In Wiscsonsin of Wisconsin Public TV. One of my former Darlington students was asked what the hardest part about bridge building was? He said it this way, "Thinking. It is all about the thinking. That is something we don't like to do very much in shop classes. Mr. Anderson tries to get us to do a lot of thinking." 

Puzzler - See picture above

Tech Vocab -  Dial calipers - Annual Rings - T x W x L - Checking