2009. Retrieved 2009-08-27. ↑ John Fry Heather Mathematical instruments: their construction, adjustment, testing, and use, comprising drawing, measuring, optical, surveying, and astronomical instruments (Crosby, Lockwood and co., 1884) pages 1-2 ↑ The American engineer Volumes 19-20, 1890 page 107 ↑ Language of the Office dictionary (in Finnish) (Web Version 1.0 ed.).