NASA, "Model Rocket Engine Performance" https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/model-rocket-engine-performance/
Dean's Benchtop, "Experimental Thrust Curve of a Water Rocket" http://www.et.byu.edu/~wheeler/benchtop/thrustcurve.php
Richard Nakka's Experimental Rocketry Web Site, "Solid Rocket Motor Theory -- Chamber Pressure" http://www.nakka-rocketry.net/th_pres.html