T-square vs folding rule

T-square

noun
  • A rule with a short perpendicular crosspiece at one end, used by draughtsmen to draw parallel lines. 

  • A sex position whereby the receiving partner lies on the back with knees up and legs apart while the penetrating partner lies on either side perpendicular to the receiver, with the penetrating partner's hips under the arch formed by receiver's legs. 

folding rule

How often have the words T-square and folding rule occurred in a corpus of books? (source: Google Ngram Viewer )