Vernier Caliper

Found this image by accident yesterday. It was taken (thx, Iona) during the inventory work in the Tapajós-Arapiuns Extractive Reserve in Brazil (see Tapajós-Arapiuns) and shows me (with beard) explaining to the field crews how to use a vernier caliper to read a dendrometer band (see How to Make Dendrometer Bands) to see how fast a tree is growing. It's a bit complicated, actually, and I was having trouble explaining how to do this with my horrible Portuguese. [NOTE: The Forest Stewardship Council cap is long gone. I left it on a chair in a restaurant in Santarem].