Back in high school, I built (with some parental assistance) an apparatus to measure how quickly the pressure would drop (in a pressurized cylinder) when a very small hole allowed air to leak out.

Turns out, not only can you measure temperature that way, but can extrapolate the graph out to find absolute zero (IIRC my result was out by about 20 kelvin, which I think is pretty damn good for a high-school-garage project).

No, there you are measuring R, assuming the air inside the cylinder was an ideal gas.