The 400 Series has a depth sensing range of 10 m but has an 'expressive range' of 65 m. It is this depth scale calculation that allows the camera to see 65 m, whilst the earlier SR300 camera model can only see around 2 m.
The default depth scale of the 400 Series makes it less accurate than the SR300 at very close range but able to see much further at long range.
Quoting from SDK 2.0's projection documentation:
The default scale of a D400 device is one millimeter, allowing for a maximum expressive range of ~65 meters. The depth scale can be modified by calling rs2_set_option(...) with RS2_OPTION_DEPTH_UNITS, which specifies the number of micrometers per one increment of depth. 1000 would indicate millimeter scale, 10000 would indicate centimeter scale, while 31 would roughly approximate the SR300's 1/32th of a millimeter scale.
