hi hamish,

i didn't know trammel's really existed, really neat:

http://www.sciencemuseum.org.uk/objects/mathematics/1876-662.aspx

this tool is awesome too:

http://www.sciencemuseum.org.uk/objects/mathematics/1909-191.aspx

i remember playing with these as a kid:

http://www.sciencemuseum.org.uk/objects/mathematics/1976-61.aspx

thanks for the links, awesome.