This is an excellent choice for your black and white treatment. This shot I presume didn't have a lot of color to begin with, so by going black and white you were able to bring out the contrast of the stone and carving. This conveys time OK, but I am not sure how this device measures time. I presume it's a sun dial of sorts, if that's the case, then a shadow showing the current time would be helpful.
Your post processing work is well done, no artifacts or oversharpening.
Tried to figure out location from the distance between marks, but I could not do it. Guessing above 45 deg. Where is it?
Nice shot. Uniform gray with the black marking and lettering is nice.