Yes it is!!! Nice catch. This is just one way to prove it's not 18% using very little math. Zone VIII isn't supposed to have specular reflections. So, it shouldn't be over 100%. As Zone VIII is three stops over Zone V and if the meter "reads" 18%, then Zone VIII is over 100%; therefore, the meter can't be reading 18%. Another photographic myth bites the dust.
Originally Posted by Bill Burk
I almost worked myself into a corner as exposure meters don't "see" Reflectance, but it's possible to extrapolate an equivalent number based on the reflection meter's and incident meter's calibration. This is also the beginning of a more precise way to determine exactly what a meter "sees". Apply the average illuminance of Daylight to the different reflection densities (basically log Reflectance), plug them into the camera exposure equation, and see which one produces the correct exposure at the metered exposure point for a given EI.
And for the record, it's 12%.