Thank ya, sir!
As for "zero lift" angle, let's take the venerable Clark Y as an example:
As used as a wing, or a propeller, when you have "zero angle" based on the flat of the airfoil, you still have 3 degrees angle of attack, due to the chord line of the airfoil. And, to confuse things more, when the chord line is at "zero" angle of attack, you still have "lift", as the airfoil is still acting to the relative wind.
Now, to REALLY throw the monkey wrench into the works: when you have a sufficient negative angle to achieve "zero lift", you still have "lift". However, it is diminished, as it is being diverted as "translational lift", i.e: the lift force is now directed in the direction of the relative wind. Ask any good Gyro Driver, or Wind Turbine engineer.
Aspirin, any one?
Thanks for the report, real measurements are always great.
FWIW, many prop mfgrs report the pitch as measured from the bottom of the blade. And, even at true zero AoA , there are normally a few degrees of pitch to go before we get to zero lift. Between these two things, it can be hard to know where the true zero lift pitch is on a particular prop.