Hi what is max number of depth in openni?

I run astra pro in python openni2
I find some code in internet and It runs well
I got depthmap by this code
dmap = np.fromstring(self.depth_stream.read_frame().get_buffer_as_uint8(), dtype=np.uint16).reshape(480, 640)

it gave me data 0 ~ around 9851

I want to know how this depth data(0~ 9851) to convert meter or mm and
I want to find some document about astra pro oppenni

You already have what you want. The data is distance from the camera in mm. Of course, I am assuming you have already done:
openni::VideoMode paramvideo;