Compass & Rule: Architecture as Mathematical Practice in England, 1500-1750, is a lovely online version of the physical exhibition held at the Museum of the History of Science, Oxford, in 2009. Compass and Rule focuses on design and drawing, exploring the role of geometry in the dramatic transformation of English architecture between the 16th and 18th centuries. During this time new concepts of design based on geometry changed how architects worked and what they built, as well as the intellectual status and social standing of their discipline. Identified as a branch of practical mathematics, architecture became the most artistic of the sciences and the most scientific of the arts.
As well as a great online exhibition covering the geometry of stonemasons, the design of St Paul's and the architectural apprenticeship of King George III, it also has some fascinating videos of how to construct technical drawings or design classical architectural features using just a straight edge, compass and right angle.