Spanogle, J. A. & Buckley, E. C. The N.A.C.A. combustion chamber gas-sampling valve and some preliminary test results, report, March 1933; (https://digital.library.unt.edu/ark:/67531/metadc54156/m1/1/: accessed July 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .